Multi-layered filter media

ABSTRACT

Fiber webs that may be used as filter media are provided. In some embodiments, the filter media may include multiple layers. Each layer may be designed to have separate functions in the filter media. For example, a first layer may be provided for improving dust holding capacity, a second layer for improving efficiency, and a third layer for providing support and strength to the media. By designing the layers to have separate functions, each layer may be optimized to enhance its function without negatively impacting the performance of another layer of the media.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/675,514, filed Nov. 13, 2012, which is incorporated herein byreference in its entirety.

FIELD OF INVENTION

The present embodiments relate generally to multi-layered filter media,and specifically, to multi-layered filter media having enhanced physicaland/or performance characteristics.

BACKGROUND

Filter elements can be used to remove contamination in a variety ofapplications. Such elements can include a filter media which may beformed of a web of fibers. The fiber web provides a porous structurethat permits fluid (e.g., gas, liquid) to flow through the media.Contaminant particles (e.g., dust particles, soot particles) containedwithin the fluid may be trapped on or in the fiber web. Depending on theapplication, the filter media may be designed to have differentperformance characteristics.

In some applications, filter media may include multiple layers. Althoughmany multi-layered filter media exist, improvements in the physicaland/or performance characteristics of the layers within the media (e.g.,strength, air resistance, efficiency, and high dust holding capacity)would be beneficial.

SUMMARY OF THE INVENTION

Multi-layered filter media having enhanced physical and/or performancecharacteristics, and related articles, components, and methodsassociated therewith, are provided. The subject matter of thisapplication involves, in some cases, interrelated products, alternativesolutions to a particular problem, and/or a plurality of different usesof structures and compositions.

In one set of embodiments, a filter media is provided. In oneembodiment, a filter media includes a first layer comprising a firstplurality of fibers, wherein the first layer has a first airpermeability and a first mean flow pore size. The filter media alsoincludes a second layer comprising a second plurality of fibers havingan average fiber diameter of less than or equal to about 1 micron,wherein the second layer has a second air permeability and a second meanflow pore size. The filter media further includes a third layercomprising a third plurality of fibers, wherein the third plurality offibers comprises cellulose fibers, and wherein the third layer has athird air permeability and a third mean flow pore size. Each of thefirst and third air permeabilities is higher than the second airpermeability and/or each of the first and third mean flow pore sizes ishigher than the second mean flow pore size. The first layer, the secondlayer, and the third layer may be discrete layers. The second layer ispositioned between the first and third layers.

In another embodiment, a filter media includes a first layer comprisinga first plurality of fibers. The filter media also includes a secondlayer comprising a second plurality of fibers. The filter media furtherincludes a third layer comprising cellulose fibers, wherein the thirdlayer has an air permeability of greater than or equal to about 400L/m²sec and less than or equal to about 2000 L/m²sec, and a Mullen Burststrength of greater than or equal to about 200 kPa and less than orequal to about 500 kPa. The second layer is positioned between the firstand third layers.

In another embodiment, a filter media includes a first layer comprisinga first plurality of fibers and a second layer comprising a secondplurality of fibers. The filter media also includes a third layer havingan air permeability greater than or equal to about 400 L/m²sec and lessthan or equal to about 2000 L/m²sec, and a Mullen Burst strength ofgreater than or equal to about 200 kPa and less than or equal to about500 kPa. The filter media further includes a fourth layer having an airpermeability greater than or equal to about 1,000 L/m²sec and less thanor equal to about 12,000 L/m²sec, a basis weight of greater than orequal to about 5 g/m² and less than or equal to about 70 g/m², and athickness of less than or equal to about 0.5 mm. The second and fourthlayers are positioned between the first and third layers, and the fourthlayer is positioned between the second and third layers.

In another embodiment, a filter media includes a first layer comprisinga first plurality of fibers, wherein the first layer has a first airpermeability and a first mean flow pore size. The filter media alsoincludes a second layer comprising a second plurality of fibers, whereinthe second layer has a second air permeability and a second mean flowpore size. The filter media further includes a third layer comprising athird plurality of fibers and a plurality of perforations. The first airpermeability is higher than the second air permeability and/or the firstmean flow pore size is higher than the second mean flow pore size.

In another embodiment, a filter media includes a first layer comprisinga plurality of fibers. The filter media also includes a second layercomprising cellulose fibers and a plurality of perforations.

In another embodiment, a filter media includes a first layer comprisinga first plurality of fibers, wherein the first plurality of fibers aresynthetic fibers formed by a meltblown process or a centrifugal spinningprocess, and wherein the first plurality of fibers has an average fiberdiameter of greater than about 1.5 microns. The filter media alsoincludes a second layer comprising a second plurality of fibers, whereinthe second plurality of fibers are synthetic fibers formed by ameltblown process or a centrifugal spinning process, and wherein thesecond plurality of fibers has an average fiber diameter of less than orequal to about 1.5 microns. The filter media further includes a thirdlayer comprising a third plurality of fibers, wherein the thirdplurality of fibers comprises cellulose fibers. The second layer ispositioned between the first and third layers.

In another set of embodiments, a method of forming a filter media isprovided. The method includes providing a first layer comprising aplurality of fibers. The method also includes providing a second layercomprising cellulose fibers and a plurality of perforations. The methodfurther includes combining the first and second layers.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1 is a schematic diagram showing a cross-section of a filter mediaaccording to one set of embodiments;

FIG. 2 is a schematic diagram showing a cross-section of a filter mediaaccording to one set of embodiments;

FIG. 3A-B are schematic diagrams showing a cross-section of a filtermedia including perforations, and a cross-section of a perforationaccording to one set of embodiments; and

FIG. 4 is a schematic diagram showing different patterns of perforationsaccording to one set of embodiments.

DETAILED DESCRIPTION

Filter media are described herein. In some embodiments, the filter mediamay include multiple layers. Each layer may be designed to havedifferent functions in the filter media. For example, a first layer maybe provided for improving dust holding capacity, a second layer forimproving efficiency, and a third layer for providing support andstrength to the media. By designing the layers to have different primaryfunctions, each layer may be optimized to enhance its function withoutsubstantially negatively impacting the performance of another layer ofthe media. Filter media, as described herein, may be particularlywell-suited for applications that involve filtering fuel, air, and lubeoil though the media may also be used in other applications (e.g.,hydraulic applications).

An example of a filter media including a plurality of layers is shown inFIG. 1. As shown illustratively in FIG. 1, a filter media 10, shown incross section, may include a first layer 15, a second layer 20, and athird layer 25. As described above, each of the layers of the media maybe designed for a particular primary purpose. For example, in one set ofembodiments, the first layer may be used for imparting good dust holdingproperties to the media, the second layer may be used as an efficiencylayer, and the third layer may be used to provide support and strengthto the media. In some such embodiments, the second layer may contain asecond plurality of fibers and may have an air permeability that islower than the air permeabilities of the first and/or third layers, aswould be expected of a layer imparting efficiency characteristics. Thethird layer may provide support and strength to the media, while havinga relatively high air permeability so as to not substantially affect theresistance across the media.

As described further below, the high air permeability of the third layermay be achieved by including perforations in the layer that reduce theresistance across the layer and/or by designing the layer to have a highair permeability and a relatively high strength. By contrast, in someexisting media, support and/or strength can be provided in the samelayer that functions as an efficiency layer; however, in certainembodiments, combining two functions in one layer to form a compositelayer may compromise the effectiveness of each function. A tradeoff, forinstance, between strength and filtration performance may exist for acomposite layer designed to have both support and efficiency functions.For example, changes to the physical structure of a composite layer tooptimize its structural support role may adversely affect the airpermeability of the layer and/or may decrease filtration efficiency.

Furthermore, in other existing filter media and/or filter elements, anon-fibrous support layer such as a layer formed of a wire or mesh isincluded to provide additional support for the filter media. Often, theextra non-fibrous support layer may have zero or little filtrationperformance and requires additional manufacturing steps and/orspecialized equipment to produce. In some cases, the use of the extralayer may increase the cost and/or difficulty of manufacturing thefilter media and/or filter element. When a layer is intended to serveone primary function, as described in certain embodiments herein, thelayer may be optimized for its particular function without compromisingthe function of other layers in the filter media. Additionally oralternatively, optimization of a layer for a particular function mayprevent the need for an additional supplemental layer with the samefunction. It should be appreciated, however, that certain embodimentsmay include a layer having more than one function.

In some embodiments in which a layer has a separate primary functionfrom another layer, the layer may be designed to be discrete from theother layer. That is, the fibers from one layer do not substantiallyintermingle with fibers from another layer. For example, with respect toFIG. 1, in one set of embodiments, fibers from the first layer do notsubstantially intermingle with fibers of the second layer. In anotherembodiment, the second layer is discrete with at least one adjacentlayer. For example, in some embodiments, fibers from the second layer donot intermingle with fibers from the third layer and/or fibers from thefirst layer. In certain embodiments, each of the first, second and thirdlayers are discrete such that fibers from one layer do not interminglewith fibers of any adjacent layer. Discrete layers may allow forseparation of function of the layers. Each discrete layer may beindividually optimized without adversely affecting the other layers inthe filter media. For example, in a filter media with a discreteefficiency layer and a discrete support layer, the support layer can beperforated to improve its structural support characteristics and airpermeability without influencing the filtration efficiency. Discretelayers may be joined by any suitable process including, for example,lamination, thermo-dot bonding, calendering, ultrasonic processes, or byadhesives, as described in more detail below.

It should be appreciated, however, that certain embodiments may includeone or more layers that are not discrete with respect to one another.For example, a first layer functioning primarily as a capacity layer anda second layer function primarily as an efficiency layer may be formedas a composite or multiphase layer.

In some embodiments, a filter media 12 may include a first layer 15, asecond layer 20, a third layer 25, and a fourth layer 30, as shownillustratively in FIG. 2. In certain embodiments, the first, second, andthird layers in FIG. 2 may be the same as the first, second, and thirdlayers, respectively, in FIG. 1. However, other configurations arepossible as one or more of the first, second, and third layers of FIG. 2may be different from those of FIG. 1 as described in more detail below.In some embodiments, the fourth layer may be a spacer layer. As shownillustratively in FIG. 2, the fourth layer which functions as a spacerlayer may be positioned between the second and third layers, however, itshould be appreciated that a spacer layer may be positioned betweenother layers (e.g., between first and second layers) in otherembodiments. A spacer layer may reduce shear forces, e.g., during apleating process, and/or may promote better flow properties. In oneexample, the spacer layer may be a spunbond layer that is adjacent to asecond layer (e.g., an efficiency layer) and/or a third layer (e.g., asupport layer).

As described herein and illustratively shown in FIG. 3A, a filter media13, shown in cross-section, may include first layer 15, second layer 20,and third layer 25. In this embodiment, the third layer may include aplurality of perforations 35 as shown illustratively in FIG. 3A and asdescribed in more detail below.

It should be understood that the configurations of the layers shown inthe figures are by way of example only, and that in other embodiments,filter media including other configurations of layers may be possible.For example, while the first, second, third (and optionally fourth)layers are shown in a specific order in FIGS. 1-3, in other embodiments,the third layer may be positioned between the first and second layers.In other embodiments, the first layer may be positioned between thesecond and third layers. Other configurations are also possible.Additionally, it should be appreciated that the terms “first”, “second”,“third” and “fourth” layers, as used herein, refer to different layerswithin the media, and are not meant to be limiting with respect to theparticular function of that layer. For example, while a “first” layermay be described as being a layer for enhancing dust holding capacity(e.g., a capacity layer) in some embodiments, in other embodiments, a“first” layer may be used to describe a layer used for enhancingefficiency (e.g., an efficiency layer), a layer for providing support(e.g., a support layer), or a layer that functions as a spacer (e.g., aspacer layer). Likewise, each of a “second”, “third” and “fourth” layermay independently be used to describe a layer for enhancing dust holdingcapacity (e.g., a capacity layer), a layer used for enhancing efficiency(e.g., an efficiency layer), a layer for providing support (e.g., asupport layer), or a layer that functions as a spacer (e.g., a spacerlayer). Additionally, a layer may have more than one such function incertain embodiments. Furthermore, in some embodiments, additional layers(e.g., “fifth”, “sixth”, or “seventh” layers) may be present in additionto the ones shown in the figures. It should also be appreciated that notall components shown in the figures need be present in some embodiments.

In some embodiments, one or more layers (or sub-layers) in the filtermedia may include synthetic fibers. Synthetic fibers may include anysuitable type of synthetic polymer. Examples of suitable syntheticfibers include staple fibers, polyesters (e.g., polyethyleneterephthalate, polybutylene terephthalate), polycarbonate, polyamides(e.g., various nylon polymers), polyaramid, polyimide, polyethylene,polypropylene, polyether ether ketone, polyolefin, acrylics, polyvinylalcohol, regenerated cellulose (e.g., synthetic cellulose such lyocell,rayon), polyacrylonitriles, polyvinylidene fluoride (PVDF), copolymersof polyethylene and PVDF, polyether sulfones, and combinations thereof.In some embodiments, the synthetic fibers are organic polymer fibers.Synthetic fibers may also include multi-component fibers (i.e., fibershaving multiple compositions such as bicomponent fibers). In some cases,synthetic fibers may include meltblown fibers, which may be formed ofpolymers described herein (e.g., polyester, polypropylene). In othercases, synthetic fibers may be electrospun fibers. The filter media, aswell as each of the layers (or sub-layers) within the filter media, mayalso include combinations of more than one type of synthetic fiber. Itshould be understood that other types of synthetic fiber types may alsobe used.

In some embodiments, the average diameter of the synthetic fibers of oneor more layers (or sub-layers) in the filter media may be, for example,greater than or equal to about 0.1 microns, greater than or equal toabout 0.3 microns, greater than or equal to about 0.5 microns, greaterthan or equal to about 1 micron, greater than or equal to about 2microns, greater than or equal to about 3 microns, greater than or equalto about 4 microns, greater than or equal to about 5 microns, greaterthan or equal to about 8 microns, greater than or equal to about 10microns, greater than or equal to about 12 microns, greater than orequal to about 15 microns, or greater than or equal to about 20 microns.In some instances, the synthetic fibers may have an average diameter ofless than or equal to about 30 microns, less than or equal to about 20microns, less than or equal to about 15 microns, less than or equal toabout 10 microns, less than or equal to about 7 microns, less than orequal to about 5 microns, less than or equal to about 4 microns, lessthan or equal to about 1.5 microns, less than or equal to about 1micron, less than or equal to about 0.8 microns, or less than or equalto about 0.5 microns. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to about 1 micron and lessthan or equal to about 5 microns). Other values of average fiberdiameter are also possible.

In some cases, the synthetic fibers may be continuous (e.g., meltblownfibers, spunbond fibers, electrospun fibers, centrifugal spun fibers,etc.). For instance, synthetic fibers may have an average length ofgreater than or equal to about 1 inch, greater than or equal to about 50inches, greater than or equal to about 100 inches, greater than or equalto about 300 inches, greater than or equal to about 500 inches, greaterthan or equal to about 700 inches, or greater than or equal to about 900inches. In some instances, synthetic fibers may have an average lengthof less than or equal to about 1000 inches, less than or equal to about800 inches, less than or equal to about 600 inches, less than or equalto about 400 inches, or less than or equal to about 100 inches.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 50 inches and less than or equal to about1000 inches). Other values of average fiber length are also possible.

In other embodiments, the synthetic fibers are not continuous (e.g.,staple fibers). For instance, in some embodiments, synthetic fibers inone or more layers (or sub-layers) in the filter media may have anaverage length of greater than or equal to about 0.5 mm, greater than orequal to about 1 mm, greater than or equal to about 2 mm, greater thanor equal to about 4 mm, greater than or equal to about 6 mm, greaterthan or equal to about 8 mm, or greater than or equal to about 10 mm. Insome instances, synthetic fibers may have an average length of less thanor equal to about 12 mm, less than or equal to about 10 mm, less than orequal to about 8 mm, less than or equal to about 6 mm, less than orequal to about 4 mm, or less than or equal to about 2 mm. Combinationsof the above-referenced ranges are also possible (e.g., greater than orequal to about 1 mm and less than or equal to about 4 mm). Other valuesof average fiber length are also possible.

In one set of embodiments, one or more layers in the filter media mayinclude bicomponent fibers. The bicomponent fibers may comprise athermoplastic polymer. Each component of the bicomponent fiber can havea different melting temperature. For example, the fibers can include acore and a sheath where the activation temperature of the sheath islower than the melting temperature of the core. This allows the sheathto melt prior to the core, such that the sheath binds to other fibers inthe layer, while the core maintains its structural integrity. Thecore/sheath binder fibers can be concentric or non-concentric. Otherexemplary bicomponent fibers can include split fiber fibers,side-by-side fibers, and/or “island in the sea” fibers.

The average diameter of the bicomponent fibers may be, for example,greater than or equal to about 1 micron, greater than or equal to about2 microns, greater than or equal to about 3 microns, greater than orequal to about 4 microns, greater than or equal to about 5 microns,greater than or equal to about 8 microns, greater than or equal to about10 microns, greater than or equal to about 12 microns, greater than orequal to about 15 microns, or greater than or equal to about 20 microns.In some instances, the bicomponent fibers may have an average diameterof less than or equal to about 30 microns, less than or equal to about20 microns, less than or equal to about 15 microns, less than or equalto about 10 microns, less than or equal to about 7 microns, less than orequal to about 5 microns, less than or equal to about 4 microns, or lessthan or equal to about 2 microns. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to about 5 micronsand less than or equal to about 15 microns). Other values of averagefiber diameter are also possible.

In some embodiments, bicomponent fibers may have an average length ofgreater than or equal to about 0.5 mm, greater than or equal to about 1mm, greater than or equal to about 2 mm, greater than or equal to about4 mm, greater than or equal to about 6 mm, greater than or equal toabout 8 mm, or greater than or equal to about 10 mm. In some instances,bicomponent fibers may have an average length of less than or equal toabout 12 mm, less than or equal to about 8 mm, less than or equal toabout 6 mm, less than or equal to about 4 mm, less than or equal toabout 2 mm, or less than or equal to about 1 mm. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 1 mm and less than or equal to about 3 mm). Other values ofaverage fiber length are also possible.

In some embodiments, one or more layers (or sub-layers) in the filtermedia may include one or more cellulose fibers, such as softwood fibers,hardwood fibers, a mixture of hardwood and softwood fibers, regeneratedcellulose fibers, and mechanical pulp fibers (e.g., groundwood,chemically treated mechanical pulps, and thermomechanical pulps).Exemplary softwood fibers include fibers obtained from mercerizedsouthern pine (e.g., mercerized southern pine fibers or “HPZ fibers”),northern bleached softwood kraft (e.g., fibers obtained from Robur Flash(“Robur Flash fibers”)), southern bleached softwood kraft (e.g., fibersobtained from Brunswick pine (“Brunswick pine fibers”)), or chemicallytreated mechanical pulps (“CTMP fibers”). For example, HPZ fibers can beobtained from Buckeye Technologies, Inc., Memphis, Tenn.; Robur Flashfibers can be obtained from Rottneros AB, Stockholm, Sweden; andBrunswick pine fibers can be obtained from Georgia-Pacific, Atlanta, Ga.Exemplary hardwood fibers include fibers obtained from Eucalyptus(“Eucalyptus fibers”). Eucalyptus fibers are commercially availablefrom, e.g., (1) Suzano Group, Suzano, Brazil (“Suzano fibers”), (2)Group Portucel Soporcel, Cacia, Portugal (“Cacia fibers”), (3) Tembec,Inc., Temiscaming, QC, Canada (“Tarascon fibers”), (4) KartonimexIntercell, Duesseldorf, Germany, (“Acacia fibers”), (5) Mead-Westvaco,Stamford, Conn. (“Westvaco fibers”), and (6) Georgia-Pacific, Atlanta,Ga. (“Leaf River fibers”).

The average diameter of the cellulose fibers in one or more layers (orsub-layers) in the filter media may be, for example, greater than orequal to about 1 micron, greater than or equal to about 2 microns,greater than or equal to about 3 microns, greater than or equal to about4 microns, greater than or equal to about 5 microns, greater than orequal to about 8 microns, greater than or equal to about 10 microns,greater than or equal to about 15 microns, greater than or equal toabout 20 microns, greater than or equal to about 30 microns, or greaterthan or equal to about 40 microns. In some instances, the cellulosefibers may have an average diameter of less than or equal to about 50microns, less than or equal to about 40 microns, less than or equal toabout 30 microns, less than or equal to about 20 microns, less than orequal to about 15 microns, less than or equal to about 10 microns, lessthan or equal to about 7 microns, less than or equal to about 5 microns,less than or equal to about 4 microns, or less than or equal to about 2microns. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 1 micron and less than or equal toabout 5 microns). Other values of average fiber diameter are alsopossible.

In some embodiments, the cellulose fibers may have an average length.For instance, in some embodiments, cellulose fibers may have an averagelength of greater than or equal to about 0.5 mm, greater than or equalto about 1 mm, greater than or equal to about 2 mm, greater than orequal to about 3 mm, greater than or equal to about 4 mm, greater thanor equal to about 5 mm, greater than or equal to about 6 mm, or greaterthan or equal to about 8 mm. In some instances, cellulose fibers mayhave an average length of less than or equal to about 10 mm, less thanor equal to about 8 mm, less than or equal to about 6 mm, less than orequal to about 4 mm, less than or equal to about 2 mm, or less than orequal to about 1 mm. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to about 1 mm and less thanor equal to about 3 mm). Other values of average fiber length are alsopossible.

In some embodiments, one or more layers in the filter media may includefibrillated fibers. As known to those of ordinary skill in the art, afibrillated fiber includes a parent fiber that branches into smallerdiameter fibrils, which can, in some instances, branch further out intoeven smaller diameter fibrils with further branching also beingpossible. The branched nature of the fibrils leads to a layer and/orfiber web having a high surface area and can increase the number ofcontact points between the fibrillated fibers and other fibers in theweb. Such an increase in points of contact between the fibrillatedfibers and other fibers and/or components of the web may contribute toenhancing mechanical properties (e.g., flexibility, strength) and/orfiltration performance properties of the layer and/or fiber web.

As noted above, fibrillated fibers include parent fibers and fibrils. Insome embodiments, the parent fibers may have an average diameter of lessthan or equal to about 75 microns, less than or equal to about 60microns, less than or equal to about 50 microns, less than or equal toabout 40 microns, less than or equal to about 30 microns, less than orequal to about 20 microns, or less than or equal to about 15 microns. Insome embodiments the parent fibers may have an average diameter ofgreater than or equal to about 10 microns, greater than or equal toabout 15 microns, greater than or equal to about 20 microns, greaterthan or equal to about 30 microns, greater than or equal to about 40microns, greater than or equal to about 50 microns, greater than orequal to about 60 microns, or greater than or equal to about 75 microns.Combinations of the above referenced ranges are also possible (e.g.,parent fibers having an average diameter of greater than or equal toabout 15 microns and less than about 75 microns). Other ranges are alsopossible.

In some embodiments, the fibrils may have an average diameter of lessthan or equal to about 15 microns, less than or equal to about 10microns, less than or equal to about 8 microns, less than or equal toabout 6 microns, less than or equal to about 4 microns, less than orequal to about 3 microns, less than or equal to about 2 microns, or lessthan or equal to about 1 micron. In some embodiments the fibrils mayhave an average diameter of greater than or equal to about 0.2 microns,greater than or equal to about 1 micron, greater than or equal to about2 microns, greater than or equal to about 3 microns, greater than orequal to about 4 microns, greater than or equal to about 6 microns,greater than or equal to about 8 microns, or greater than or equal toabout 10 microns. Combinations of the above referenced ranges are alsopossible (e.g., fibrils having an average diameter of greater than orequal to about 3 microns and less than about 6 microns). Other rangesare also possible.

In some embodiments, the average length of a fibrillated fiber may beless than or equal to about 10 mm, less than or equal to about 8 mm,less than or equal to about 6 mm, less than or equal to about 5 mm, lessthan or equal to about 4 mm, less than or equal to about 3 mm, or lessthan or equal to about 2 mm. In certain embodiments, the average lengthof fibrillated fibers may be greater than or equal to about 1 mm,greater than or equal to about 2 mm, greater than or equal to about 4mm, greater than or equal to about 5 mm, greater than equal to about 6mm, or greater than or equal to about 8 mm. Combinations of the abovereferenced ranges are also possible (e.g., fibrillated fibers having anaverage length of greater than or equal to about 4 mm and less thanabout 6 mm). Other ranges are also possible. The average length of thefibrillated fibers refers to the average length of parent fibers fromone end to an opposite end of the parent fibers. In some embodiments,the maximum average length of the fibrillated fibers falls within theabove-noted ranges. The maximum average length refers to the average ofthe maximum dimension along one axis of the fibrillated fibers(including parent fibers and fibrils). It should be understood that, incertain embodiments, the fibers and fibrils may have dimensions outsidethe above-noted ranges.

The level of fibrillation of the fibrillated fibers may be measuredaccording to any number of suitable methods. For example, the level offibrillation can be measured according to a Canadian Standard Freeness(CSF) test, specified by TAPPI test method T 227 om 09 Freeness of pulp.The test can provide an average CSF value. In some embodiments, theaverage CSF value of the fibrillated fibers may vary between about 10 mLand about 750 mL. In certain embodiments, the average CSF value of thefibrillated fibers used in a fiber web may be greater than or equal toabout 10 mL, greater than or equal to about 50 mL, greater than or equalto about 100 mL, greater than or equal to about 200 mL, greater than orequal to about 400 mL, greater than or equal to about 600 mL, or greaterthan or equal to about 700 mL. In some embodiments, the average CSFvalue of the fibrillated fibers may be less than or equal to about 800mL, less than or equal to about 600 mL, less than or equal to about 400mL, less than or equal to about 200 mL, less than or equal to about 100mL, or less than or equal to about 50 mL. Combinations of theabove-referenced ranges are also possible (e.g., an average CSF value offibrillated fibers of greater than or equal to about 10 mL and less thanor equal to about 300 mL). Other ranges are also possible. The averageCSF value of the fibrillated fibers may be based on one type offibrillated fiber or more than one type of fibrillated fiber.

In some embodiments, one or more layers (or sub-layers) in the filtermedia may include glass fibers (e.g., microglass fibers, chopped strandglass fibers, or a combination thereof). Microglass fibers and choppedstrand glass fibers are known to those skilled in the art. One skilledin the art is able to determine whether a glass fiber is microglass orchopped strand by observation (e.g., optical microscopy, electronmicroscopy). Microglass fibers may also have chemical differences fromchopped strand glass fibers. In some cases, though not required, choppedstrand glass fibers may contain a greater content of calcium or sodiumthan microglass fibers. For example, chopped strand glass fibers may beclose to alkali free with high calcium oxide and alumina content.Microglass fibers may contain 10-15% alkali (e.g., sodium, magnesiumoxides) and have relatively lower melting and processing temperatures.The terms refer to the technique(s) used to manufacture the glassfibers. Such techniques impart the glass fibers with certaincharacteristics. In general, chopped strand glass fibers are drawn frombushing tips and cut into fibers in a process similar to textileproduction. Chopped strand glass fibers are produced in a morecontrolled manner than microglass fibers, and as a result, choppedstrand glass fibers will generally have less variation in fiber diameterand length than microglass fibers. Microglass fibers are drawn frombushing tips and further subjected to flame blowing or rotary spinningprocesses. In some cases, fine microglass fibers may be made using aremelting process. In this respect, microglass fibers may be fine orcoarse. As used herein, fine microglass fibers are less than or equal to1 micron in diameter and coarse microglass fibers are greater than orequal to 1 micron in diameter.

The microglass fibers may have small diameters. For instance, in someembodiments, the average diameter of the microglass fibers may be lessthan or equal to about 9 microns, less than or equal to about 7 microns,less than or equal to about 5 microns, less than or equal to about 3microns, or less than or equal to about 1 micron. In some instances, themicroglass fibers may have an average fiber diameter of greater than orequal to about 0.1 microns, greater than or equal to about 0.3 microns,greater than or equal to about 1 micron, greater than or equal to about3 microns, or greater than or equal to about 7 microns. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to about 0.1 microns and less than or equal to about 9 microns).Other values of average fiber diameter are also possible. Averagediameter distributions for microglass fibers are generally log-normal.However, it can be appreciated that microglass fibers may be provided inany other appropriate average diameter distribution (e.g., Gaussiandistribution).

In some embodiments, the average length of microglass fibers may be lessthan or equal to about 10 mm, less than or equal to about 8 mm, lessthan or equal to about 6 mm, less than or equal to about 5 mm, less thanor equal to about 4 mm, less than or equal to about 3 mm, or less thanor equal to about 2 mm. In certain embodiments, the average length ofmicroglass fibers may be greater than or equal to about 1 mm, greaterthan or equal to about 2 mm, greater than or equal to about 4 mm,greater than or equal to about 5 mm, greater than equal to about 6 mm,or greater than or equal to about 8 mm. Combinations of the abovereferenced ranges are also possible (e.g., microglass fibers having anaverage length of greater than or equal to about 4 mm and less thanabout 6 mm). Other ranges are also possible.

In other embodiments, the microglass fibers may vary significantly inlength as a result of process variations. For instance, in someembodiments, the average aspect ratios (length to diameter ratio) of themicroglass fibers in a layer (or sub-layer) may be greater than or equalto about 100, greater than or equal to about 200, greater than or equalto about 300, greater than or equal to about 1000, greater than or equalto about 3,000, greater than or equal to about 6,000, greater than orequal to about 9,000. In some instances, the microglass fibers may havean average aspect ratio of less than or equal to about 10,000, less thanor equal to about 5,000, less than or equal to about 2,500, less than orequal to about 600, or less than or equal to about 300. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to about 200 and less than or equal to about 2,500). Other valuesof average aspect ratio are also possible. It should be appreciated thatthe above-noted dimensions are not limiting and that the microglassfibers may also have other dimensions.

In general, chopped strand glass fibers may have an average fiberdiameter that is greater than the diameter of the microglass fibers. Forinstance, in some embodiments, the average diameter of the choppedstrand glass fibers may be greater than or equal to about 5 microns,greater than or equal to about 7 microns, greater than or equal to about9 microns, greater than or equal to about 11 microns, or greater than orequal to about 20 microns. In some instances, the chopped strand glassfibers may have an average fiber diameter of less than or equal to about30 microns, less than or equal to about 25 microns, less than or equalto about 15 microns, less than or equal to about 12 microns, or lessthan or equal to about 10 microns. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to about 5 micronsand less than or equal to about 12 microns). Other values of averagefiber diameter are also possible. Chopped strand diameters tend tofollow a normal distribution. Though, it can be appreciated that choppedstrand glass fibers may be provided in any appropriate average diameterdistribution (e.g., Gaussian distribution).

In some embodiments, chopped strand glass fibers may have a length inthe range of between about 0.125 inches and about 1 inch (e.g., about0.25 inches, or about 0.5 inches). In some embodiments, the averagelength of chopped strand glass fibers may be less than or equal to about1 inch, less than or equal to about 0.8 inches, less than or equal toabout 0.6 inches, less than or equal to about 0.5 inches, less than orequal to about 0.4 inches, less than or equal to about 0.3 inches, orless than or equal to about 0.2 inches. In certain embodiments, theaverage length of chopped strand glass fibers may be greater than orequal to about 0.125 inches, greater than or equal to about 0.2 inches,greater than or equal to about 0.4 inches, greater than or equal toabout 0.5 inches, greater than equal to about 0.6 inches, or greaterthan or equal to about 0.8 inches. Combinations of the above referencedranges are also possible (e.g., chopped strand glass fibers having anaverage length of greater than or equal to about 0.125 inches and lessthan about 1 inch). Other ranges are also possible.

It should be appreciated that the above-noted dimensions are notlimiting and that the microglass and/or chopped strand fibers, as wellas the other fibers described herein, may also have other dimensions.

In certain embodiments the third layer (e.g., a support layer) mayinclude a plurality of perforations as illustrated in FIG. 3A. In someinstances, the discrete nature of the layer may allow it to beperforated without altering or influencing other layers in the filtermedia. Additionally, perforations in the layer may allow the use of abroad range of fiber compositions well-suited for support applications,and may even allow the use of fiber compositions that typically wouldnot have been used (or used in large amounts) in filter media. Moreover,a wet laid layer with an exceptionally tight structure may have too lowof an air permeability that prohibits its use in most filter media.Introducing perforations into the layer may impart high airpermeability, while allowing the layer to maintain good supportcharacteristics. In another example, perforating a tight structurallayer with compact internal structure and high air resistance mayproduce a relatively open structural layer with low air resistance.Perforating the layer may also enhance its pleat stability and/orstructural support characteristics.

In some embodiments, perforating a layer may result in a plurality ofholes through the full thickness of the layer. In one embodiment,perforation 35, as shown illustratively in cross-section in FIG. 3B, maydefine a hole 40. In some embodiments, e.g., depending on the method offorming the protrusions, a structural formation 45 (e.g., a concavestructural formation) may be included on one face of the hole, andanother structural formation 50 (e.g., a convex structural formation)may be included on the other face of the hole. In certain embodiments,the hole and the structural formations may be produced by theapplication of force 62 to a surface 65 of the layer, e.g., during theperforating process. After perforation, a structural formation (e.g., aconcave structural formation) may exist around the hole on the surfacewhere the force was applied. A structural formation (e.g., a convexstructural formation) may exist around the hole on the opposite surface70. In some instances, a structural formation may include displacedmaterial that protrudes outward from a surface of the layer (i.e., awayfrom the interior of the layer), referred to herein as a protrusion. Thepresence of a protrusion may indicate that a layer has been subjected toa perforation process. It should be appreciated, however, that not allperforations need to include structural formations (e.g., a concavestructural formation and/or a convex structural formation), and/orprotrusions, and that perforations without such structural formationsand/or protrusions are also possible in some embodiments. For example, aperforation formed by the application of thermal energy (e.g., a laser)may produce a hole without any such structural formations and/orprotrusions.

As noted above, perforations may enhance the pleat stability of filtermedia that are subjected to a pleating process. For example, theprotrusions may function as a structural spacer between the pleats whichmay help prevent pleat collapse. Optionally, as described in more detailbelow, a layer impregnated with a resin and subjected to a perforationprocess may include protrusions that are strengthened with the resin.This configuration of the protrusions may also aid in preventing pleatcollapse.

In certain embodiments, a perforation may have defined attributes, suchas shape, size, aspect ratio, length, and/or width. For example, eachperforation in the plurality of perforations may have a defined shape,which may be, for example, substantially circular, square, rectangular,trapezoidal, polygonal or oval in cross-section and/or in plan view(i.e., viewed from above). The shapes may be regular or irregular. Othershapes are also possible.

In some instances, the average diameter of the perforations (e.g.,average diameter of the holes) may be measured at a surface of the layerincluding the perforations. In some embodiments, the average diameter ofthe perforations may be substantially similar throughout theperforation. For instance, in some embodiments, the average diameter maybe greater than or equal to about 0.5 mm, greater than or equal to about1.0 mm, greater than or equal to about 2 mm, greater than or equal toabout 3 mm, greater than or equal to about 4 mm, greater than or equalto about 6 mm, or greater than or equal to about 8 mm. In someinstances, the plurality of perforations may have an average diameter ofless than or equal to about 10 mm, less than or equal to about 8 mm,less than or equal to about 6 mm, less than or equal to about 4 mm, lessthan or equal to about 3 mm, or less than or equal to about 2 mm.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 2 mm and less than or equal to about 3mm). Other values of average diameter are also possible.

In other instances, the perforations may be characterized by the averageaspect ratio (i.e., a ratio of length to width) of the perforations(e.g., measured at a surface of the layer including the perforations).For instance, in some embodiments, the perforations may have an averageaspect ratio of greater than or equal to about 1.0, greater than orequal to about 1.3, greater than or equal to about 1.5, greater than orequal to about 2.0, or greater than or equal to about 2.5. In someinstances, the plurality of perforations may have an average aspectratio of less than or equal to about 5, less than or equal to about 3,less than or equal to about 2.5, less than or equal to about 2, or lessthan or equal to about 1.5. Combinations of the above-referenced rangesare also possible (e.g., an average aspect ratio of greater than orequal to about 1 and less than or equal to about 1.5). Other values ofaverage aspect ratio are also possible.

In general, a perforation may have any suitable combination of shape,size, and aspect ratio to achieve the desired properties.

The perforations may also be characterized by the average length and/oraverage width of any protrusions present adjacent the perforations. Thelength of a protrusion may be characterized by the longest dimension ofthe protrusion, and the width may be characterized by the distanceperpendicular to the length at the half-length of the protrusion. Insome embodiments, the perforations may have an average protrusion lengthof greater than or equal to about 0.5 mm, greater than or equal to about1.0 mm, greater than or equal to about 2 mm, greater than or equal toabout 3 mm, greater than or equal to about 4 mm, greater than or equalto about 5 mm, or greater than or equal to about 8 mm. In someinstances, the perforations may have an average protrusion length ofless than or equal to about 10 mm, less than or equal to about 8 mm,less than or equal to about 5 mm, less than or equal to about 4 mm, lessthan or equal to about 3 mm, or less than or equal to about 2 mm.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 1 mm and less than or equal to about 5mm). Other values of average protrusion length are also possible.

Additionally, in some embodiments the perforations may have an averageprotrusion width of greater than or equal to about 0.5 mm, greater thanor equal to about 1.0 mm, greater than or equal to about 2 mm, greaterthan or equal to about 3 mm, greater than or equal to about 4 mm,greater than or equal to about 5 mm, or greater than or equal to about 8mm. In some instances, the perforations may have an average protrusionwidth of less than or equal to about 10 mm, less than or equal to about8 mm, less than or equal to about 5 mm, less than or equal to about 4mm, less than or equal to about 3 mm, or less than or equal to about 2mm. Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 1 mm and less than or equal to about 5mm). Other values of average protrusion width are also possible. In someembodiments, the protrusions have substantially the same widths andlengths (e.g., protrusions in the shape of a square).

In embodiments, the perforations may be arranged such that a definedperiodicity (i.e., distance between the geometric centers of neighboringperforations) and/or pattern exists in the layer. The periodicity may bemeasured in the machine direction and/or in the cross direction. In someembodiments, the perforations may have an average periodicity of greaterthan or equal to about 2 mm, greater than or equal to about 5 mm,greater than or equal to about 10 mm, greater than or equal to about 12mm, greater than or equal to about 15 mm, greater than or equal to about20 mm, or greater than or equal to about 28 mm. In some instances, theperforations may have an average periodicity of less than or equal toabout 30 mm, less than or equal to about 22 mm, less than or equal toabout 18 mm, less than or equal to about 14 mm, less than or equal toabout 10 mm, or less than or equal to about 6 mm. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 5 mm and less than or equal to about 20 mm). Other values ofaverage periodicity are also possible.

In some embodiments, the periodicity of the perforations may be regularacross the layer. In other embodiments, the periodicity of theperforations may be irregular and/or may vary based on a certainfactors, such as location in the layer or the pattern of theperforations. In certain embodiments, as illustrated in FIG. 4, theplurality of perforations may be arranged to form a pattern. In someembodiments, the pattern of perforations 35 may be simple, such as acheckerboard pattern 55, or more complex like a honeycomb pattern 60shown in FIG. 4. In other cases, for example, the pattern may be cubic,hexagonal, and/or polygonal. In general, any suitable pattern can beused to achieve the desired properties. It should be noted, however,that the plurality of perforations may not have a defined pattern and/orperiodicity in some embodiments.

In certain embodiments, the perforations may cover a certain percentageof the surface area of a layer (i.e., the combined surface area of theperforations as a percentage of the total area of the layer as measuredby its length times width). For instance, in some embodiments, theperforations may cover greater than or equal to about 1%, greater thanor equal to about 3%, greater than or equal to about 5%, greater than orequal to about 8%, greater than or equal to about 10%, greater than orequal to about 15%, greater than or equal to about 20%, or greater thanor equal to about 25% of the surface area of the layer. In someinstances, perforations may cover less than or equal to about 30%, lessthan or equal to about 25%, less than or equal to about 20%, less thanor equal to about 15%, less than or equal to about 10%, or less than orequal to about 5% of the surface area of the layer. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 5% and less than or equal to about 20%). Other ranges ofcoverage are also possible.

In some embodiments, it should be understood that the third layer neednot include any perforations.

Regardless of whether or not the third layer includes perforations, insome embodiments, the third layer may be substantially joined to atleast one layer (e.g., a first layer, a second layer, and/or a fourthlayer) in the filter media (e.g., by lamination, point bonding,thermo-dot bonding, ultrasonic bonding, calendering, use of adhesives(e.g., glue-web), and/or co-pleating). A substantially joined layer mayhave, for example, greater than equal to about 25%, greater than equalto about 50%, greater than equal to about 75%, or greater than equal toabout 90% of its surface in contact with another layer of the filtermedia. In some embodiments, 100% of the surface of the layer may be incontact with another layer.

Moreover, regardless of whether or not the third layer includesperforations, the layer may be a measurable weight percentage of theentire filter media. For instance, in some embodiments, the weightpercentage of the third layer in the entire filter media may be greaterthan or equal to about 10 wt %, greater than or equal to about 25 wt %,greater than or equal to about 35 wt %, greater than or equal to about45 wt %, greater than or equal to about 55 wt %, greater than or equalto about 65 wt %, or greater than or equal to about 75 wt %. In someinstances, the weight percentage of the third layer in the entire filtermedia may be less than or equal to about 80 wt %, less than or equal toabout 65 wt %, less than or equal to about 50 wt %, less than or equalto about 40 wt %, less than or equal to about 30 wt %, or less than orequal to about 20 wt %. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to about 25 wt % and lessthan or equal to about 65 wt %). Other values of weight percentage ofthe third layer in the entire filter media are also possible.

The third layer (e.g., a support layer) may include a plurality offibers. In general, a number of different materials can be used to formthe fibers as described below. In some embodiments, the fibers are madefrom cellulose. Examples of cellulose fibers are provided above.

In some cases, the third layer (e.g., support layer) may have a specificweight percentage of cellulose fibers. For instance, in someembodiments, the weight percentage of cellulose fibers in the thirdlayer may be greater than or equal to about 40%, greater than or equalto about 55%, greater than or equal to about 70%, greater than or equalto about 75%, greater than or equal to about 80%, or greater than orequal to about 90%. In some instances, the weight percentage ofcellulose fibers in the third layer may be less than or equal to about100%, less than or equal to about 85%, less than or equal to about 75%,less than or equal to about 65%, or less than or equal to about 55%.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 70% and less than or equal to about 80%).In some embodiments, 100% of the fibers in the third layer are cellulosefibers. Other values of weight percentage of the cellulose fibers in thethird layer are also possible.

In certain embodiments, the use of cellulose fibers may allow the layerto be specifically optimized for a particular filter media application.In one example, cellulose fibers may allow the surface chemistry of thelayer to be easily modified (e.g., by hydrophobic surface treatments) tobe well-suited for filtration (e.g., air filtration). Cellulose fibersmay also allow the resin to be selected based on properties other thanstructural support, such as pleat-ability. In other embodiments,cellulose fibers may be obtained from a recycling process. For example,a layer may be produced using material (e.g., fibers) from recycledpaper.

In addition to the cellulose fibers described above, the third layer mayalso include one or more of glass fibers, synthetic fibers, bicomponentfibers, and/or fibrillated fibers. Alternatively, in other embodiments,the third layer may include glass fibers, synthetic fibers, bicomponentfibers, and/or fibrillated fibers in lieu of cellulose fibers. Forinstance, in some embodiments, the weight percentage of each of glassfibers, synthetic fibers, bicomponent fibers, and/or fibrillated fibersin the third layer may independently be greater than or equal to about0%, greater than or equal to about 0.1%, greater than or equal to about1%, greater than or equal to about 2%, greater than or equal to about5%, greater than or equal to about 10%, greater than or equal to about15%, greater than or equal to about 20%, greater than or equal to about30%, or greater than or equal to about 40%. In some instances, theweight percentage of each of the glass fibers, synthetic fibers,bicomponent fibers, and/or fibrillated fibers in the third layer mayindependently be less than or equal to about 50%, less than or equal toabout 40%, less than or equal to about 30%, less than or equal to about20%, less than or equal to about 15%, less than or equal to about 10%,less than or equal to about 5%, less than or equal to about 2%, lessthan or equal to about 0.5%, or less than or equal to about 0.1%.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 0% and less than or equal to about 20%).Other values of weight percentages of the fibers in the third layer arealso possible. Examples of glass fibers, synthetic fibers, andbicomponent fibers are provided in more detail herein. In one example,the third layer may contain synthetic (e.g., polyester) fibers toincrease the durability of the layer.

In some cases, the average diameter of the fibers in the third layer maybe larger than the average diameter of the fibers in one or more otherlayers of the filter media (e.g., a first, a second, and/or a fourthlayer). In one example, the average diameter of the fibers in the thirdlayer may be larger than the average diameter of fibers in a first layer(e.g., a capacity layer) and/or a second layer (e.g., an efficiencylayer). In some embodiments, a plurality of fibers in the third layermay have an average diameter of greater than or equal to about 20microns, greater than or equal to about 25 microns, greater than orequal to about 30 microns, greater than or equal to about 32 microns,greater than or equal to about 34 microns, greater than or equal toabout 36 microns, or greater than or equal to about 40 microns. In someinstances, the plurality of fibers may have an average diameter of lessthan or equal to about 50 microns, less than or equal to about 40microns, less than or equal to about 38 microns, less than or equal toabout 35 microns, less than or equal to about 33 microns, or less thanor equal to about 25 microns. Combinations of the above-referencedranges are also possible (e.g., an average diameter of greater than orequal to about 30 microns and less than or equal to about 40 microns).Other values of average fiber diameter are also possible.

In some embodiments, fibers in the third layer may have an averagelength of greater than or equal to about 0.5 mm, greater than or equalto about 1 mm, greater than or equal to about 2 mm, greater than orequal to about 3 mm, greater than or equal to about 4 mm, greater thanor equal to about 6 mm, or greater than or equal to about 8 mm. In someinstances, the plurality of fibers may have an average length of lessthan or equal to about 10 mm, less than or equal to about 8 mm less thanor equal to about 7 mm, less than or equal to about 5 mm, less than orequal to about 3 mm, less than or equal to about 2 mm, or less than orequal to about 1 mm. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to about 1 mm and less thanor equal to about 3 mm). Other values of average fiber length are alsopossible.

The third layer, in addition to a plurality of fibers, may also includeother components, such as a resin, surface treatments, and/or additives.In general, any suitable resin may be used to achieve the desiredproperties. For example, the resin may be polymeric, water-based, orsolvent-based. In certain embodiments, the resin may also includeadditives, such as flame retardants, hydrophobic additives, and/orhydrophilic additives. In some cases, the additives in the third layermay include viscose, nanoparticles, zeolite, and/or diamaceous earth.

The third layer (e.g., a support layer), as described herein, may havecertain structural characteristics, such as basis weight, thickness, anddensity. For instance, in some embodiments, the third layer may have abasis weight of greater than or equal to about 50 g/m², greater than orequal to about 75 g/m², greater than or equal to about 90 g/m², greaterthan or equal to about 105 g/m², greater than or equal to about 120g/m², greater than or equal to about 135 g/m², or greater than or equalto about 175 g/m². In some instances, the third layer may have a basisweight of less than or equal to about 200 g/m², less than or equal toabout 150 g/m², less than or equal to about 130 g/m², less than or equalto about 110 g/m², less than or equal to about 100 g/m², or less than orequal to about 85 g/m². Combinations of the above-referenced ranges arealso possible (e.g., a basis weight of greater than or equal to about 75g/m² and less than or equal to about 150 g/m²). Other values of basisweight are also possible. The basis weight may be determined accordingto the standard ISO 536.

The thickness of the third layer may be selected as desired. Forinstance, in some embodiments, the third layer may have a thickness ofgreater than or equal to about 0.1 mm, greater than or equal to about0.2 mm, greater than or equal to about 0.3 mm, greater than or equal toabout 0.4 mm, greater than or equal to about 0.5 mm, greater than orequal to about 1.0 mm, or greater than or equal to about 1.5 mm. In someinstances, the third layer may have a thickness of less than or equal toabout 2.0 mm, less than or equal to about 1.2 mm, less than or equal toabout 0.5 mm, less than or equal to about 0.4 mm, less than or equal toabout 0.3 mm, or less than or equal to about 0.2 mm. Combinations of theabove-referenced ranges are also possible (e.g., a thickness of greaterthan or equal to about 0.2 mm and less than or equal to about 0.5 mm).Other values of thickness are also possible. The thickness may bedetermined according to the standard ISO 534 at 2 N/cm². The density ofthe third layer may also vary as desired. For instance, in someembodiments, the third layer may have a density of greater than or equalto about 0.5 kg/m³, greater than or equal to about 0.75 kg/m³, greaterthan or equal to about 0.9 kg/m³, greater than or equal to about 1.05kg/m³, greater than or equal to about 1.15 kg/m³, greater than or equalto about 1.35 kg/m³, or greater than or equal to about 1.75 kg/m³. Insome instances, the third layer may have a density of less than or equalto about 2.0 kg/m³, less than or equal to about 1.50 kg/m³, less than orequal to about 1.25 kg/m³, less than or equal to about 1.1 kg/m³, lessthan or equal to about 1.0 kg/m³, or less than or equal to about 0.85kg/m³. Combinations of the above-referenced ranges are also possible(e.g., a density of greater than or equal to about 0.75 kg/m³ and lessthan or equal to about 1.25 kg/m³). Other values of density are alsopossible. The density of the third layer may be calculated from thestandards ISO 536 and ISO 534 at 2 N/cm².

The mean flow pore size may be selected as desired. For instance, insome embodiments, the third layer may have a mean flow pore size ofgreater than or equal to about 30 microns, greater than or equal toabout 40 microns, greater than or equal to about 45 microns, greaterthan or equal to about 50 microns, greater than or equal to about 55microns, greater than or equal to about 60 microns, greater than orequal to about 65 microns, or greater than or equal to about 70 microns.In some instances, the third layer may have an average mean flow poresize of less than or equal to about 80 microns, less than or equal toabout 70 microns, less than or equal to about 60 microns, less than orequal to about 50 microns, or less than or equal to about 40 microns.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 50 microns and less than or equal toabout 60 microns). Other values of average mean flow pore size are alsopossible. The mean flow pore size may be determined according to thestandard ASTM E1294 (2008) (M.F.P.). In some embodiments, the thirdlayer may have a larger mean flow pore size than that of the secondlayer.

The third layer (e.g., a support layer), as described herein, may haveadvantageous performance properties as described herein. For instance,in some embodiments, the third layer, which may optionally include aplurality of perforations as described herein, may have a relativelyhigh dry Mullen Burst strength. The dry Mullen Burst strength may be,for example, greater than or equal to about 100 kPa, greater than orequal to about 200 kPa, greater than or equal to about 250 kPa, greaterthan or equal to about 300 kPa, greater than or equal to about 350 kPa,greater than or equal to about 400 kPa, greater than or equal to about450 kPa, or greater than or equal to about 500 kPa. In some instances,the third layer may have a dry Mullen Burst strength of less than orequal to about 500 kPa, less than or equal to about 400 kPa, less thanor equal to about 300 kPa, or less than or equal to about 200 kPa.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 100 kPa and less than or equal to about500 kPa). Other values of dry Mullen Burst strength are also possible.The dry Mullen Burst strength may be determined according to thestandard DIN 53141.

In some embodiments, the third layer (e.g., a support layer), which mayoptionally include a plurality of perforations as described herein, mayhave an air permeability greater than the air permeability of one ormore other layers in the filter media. For example, the air permeabilityof the third layer, may be at least 10 times, at least 20 times, atleast 30 times, at least 40 times, or at least 50 times greater than theair permeability of another layer in the filter media (e.g., the first,second, and/or fourth layer). In some cases, the air permeability of thethird layer may be less than or equal to 100 times than the airpermeability of another layer in the filter media (e.g., the first,second, and/or fourth layer). For instance, in some embodiments, thethird layer may have an air permeability of greater than or equal toabout 15 L/m²sec, greater than or equal to about 200 L/m²sec, greaterthan or equal to about 400 L/m²sec, greater than or equal to about 600L/m²sec, greater than or equal to about 800 L/m²sec, greater than orequal to about 1000 L/m²sec, greater than or equal to about 1200L/m²sec, greater than or equal to about 1500 L/m²sec, or greater than orequal to about 1800 L/m²sec. In some instances, the third layer may havean air permeability of less than or equal to about 2000 L/m²sec, lessthan or equal to about 1500 L/m²sec, less than or equal to about 1000L/m²sec, or less than or equal to about 600 L/m²sec. Combinations of theabove-referenced ranges are also possible (e.g., an air permeability ofgreater than or equal to about 400 L/m²sec and less than or equal toabout 800 L/m²sec). Other values of air permeability are also possible.The air permeability may be determined according to standard EN/ISO 9327(where the measurement area is 20 cm² at a 2 mbar differentialpressure).

The pressure drop across the third layer, which may optionally include aplurality of perforations as described herein, may be selected asdesired. For instance, in some embodiments, the third layer may have apressure drop of less than or equal to about 50 Pa, less than or equalto about 35 Pa, less than or equal to about 28 Pa, less than or equal toabout 22 Pa, less than or equal to about 16 Pa, less than or equal toabout 10 Pa, less than or equal to about 5 Pa, or less than or equal toabout 2 Pa. In some instances, the third layer may have a pressure dropof greater than or equal to about 1 Pa, greater than or equal to about10 Pa, greater than or equal to about 20 Pa, greater than or equal toabout 26 Pa, greater than or equal to about 30 Pa, or greater than orequal to about 40 Pa. Combinations of the above-referenced ranges arealso possible (e.g., a pressure drop of greater than or equal to about20 Pa and less than or equal to about 30 Pa). Other values of pressuredrop are also possible. The pressure drop, as described herein, can bedetermined at 10.5 FPM face velocity using a TSI 8130 filtration tester.

In some embodiments, the third layer (e.g., a support layer), which mayoptionally include perforations as described herein, may have arelatively low efficiency compared to one or more other layers in thefilter media. For instance, in some embodiments, the third layer mayhave an efficiency of less than or equal to about 50%, less than orequal to about 40%, less than or equal to about 30%, less than or equalto about 20%, less than or equal to about 10%, or less than or equal toabout 2% The efficiency may be determined according to standard ISO19438. As described in more detail below, efficiency can be measured atdifferent particle sizes (e.g., for x micron or greater particles, wherex is described below), and the above ranges of efficiency may besuitable for the various particle sizes described herein. In someembodiments, x is 4 microns such that the above ranges of efficiency aresuitable for filtering out 4 micron or larger particles.

In some embodiments, the third layer may have a relatively low dustholding capacity compared to one or more other layers in the filtermedia. For instance, in some embodiments, the third layer may have adust holding capacity of greater than or equal to about 3 g/m² (e.g.,greater than or equal to about 10 g/m², greater than or equal to about20 g/m², or greater than or equal to about 30 g/m²) and/or less than orequal to about 40 g/m² (e.g., less than or equal to about 35 g/m², lessthan or equal to about 30 g/m², less than or equal to about 25 g/m² orless than or equal to about 20 g/m²) The dust holding capacity may bedetermined according to standard ISO 19438.

The dust holding capacity and efficiency, as referred to herein, istested based on a Multipass Filter Test following the ISO 19438procedure on a Multipass Filter Test Stand manufactured by FTI. The testmay be run under different conditions. The testing uses ISO 12103-A3medium grade test dust at a base upstream gravimetric dust level (BUGL)of 50 mg/liter. The test fluid is Aviation Hydraulic Fluid AERO HFA MILH-5606A manufactured by Mobil. The test is run at a face velocity of0.06 cm/s until a terminal pressure of 100 kPa. Unless otherwise stated,the dust holding capacity values and/or efficiency values describedherein are determined at a BUGL of 50 mg/L, a face velocity of 0.06cm/s, and a terminal pressure of 100 kPa.

As described herein, in some embodiments, the third layer (e.g., supportlayer) may include cellulose fibers. The cellulose fibers may have anaverage diameter of, for example, greater than or equal to about 20microns and less than or equal to about 50 microns (e.g., greater thanor equal to about 30 microns and less than or equal to about 40microns), and an average fiber length of, for example, greater than orequal to about 1 mm and less than or equal to about 10 mm. In somecases, the third layer may include a relatively high weight percentageof cellulose fibers (e.g., greater than or equal to 70 wt %, or greaterthan or equal to 95 wt % cellulose fibers). In one embodiment, the thirdlayer may include 100 wt % cellulose fibers. The third layer may includeperforations in some embodiments, but do not include perforations inother embodiments. When perforations are present, the perforations maycover a certain percentage of the surface area of the layer. Forexample, the perforations may cover greater than or equal to about 5%and less than or equal to about 20% of the surface area of the layer.The perforations may have a periodicity of, for example, greater than orequal to about 5 mm and less than or equal to about 20 mm. The averagediameter of the perforations may be, for example, greater than or equalto about 0.5 mm and less than or equal to about 5 mm. In some instances,the third layer may be a single layer and may have a thickness ofgreater than or equal to about 0.1 mm and less than or equal to about0.5 mm (e.g., greater than or equal to about 0.2 mm and less than orequal to about 0.4 mm). The basis weight of the third layer may be, forexample, greater than or equal to about 75 g/m² and less than or equalto 150 g/m². The dry Mullen Burst strength of the third layer may be,for example, greater than or equal to about 100 kPa and less than orequal to about 500 kPa (e.g., greater than or equal to about 200 kPa andless than or equal to about 300 kPa). In some cases, the third layer mayhave a mean flow pore size of greater than 40 microns, for example,greater than or equal to 50 microns and less than or equal to 60microns. The air permeability of the third layer may be, for example,greater than or equal to about 400 L/m²sec and less than or equal toabout 1500 L/m²sec. In some instances, the third layer may have a highermean flow pore size and/or a higher air permeability than those of thesecond layer.

As described herein, a filter media may include a first layer (e.g., acapacity layer). In some embodiments, the first layer functions toenhance the dust holding capacity of the filter media, and may bereferred to as a capacity layer. In some embodiments, the first layermay include a plurality of fibers. In general, the materials that can beused to form the plurality of fibers of the first layer (e.g., acapacity layer) can vary as described below. In certain embodiments, thefirst layer may include one or more of a synthetic fiber, a bicomponentfiber, a cellulose fiber (e.g., natural cellulose, regenerated fibers),fibrillated fiber, and/or a glass fiber.

In some embodiments, in which synthetic fibers are included in the firstlayer, the weight percentage of synthetic fibers in the first layer maybe greater than or equal to about 1%, greater than or equal to about20%, greater than or equal to about 40%, greater than or equal to about60%, greater than or equal to about 80%, greater than or equal to about90%, or greater than or equal to about 95%. In some instances, theweight percentage of the synthetic fibers in the first layer may be lessthan or equal to about 100%, less than or equal to about 98%, less thanor equal to about 85%, less than or equal to about 75%, less than orequal to about 50%, or less than or equal to about 10%. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to about 80% and less than or equal to about 100%). Other valuesof weight percentage of synthetic fibers in the first layer are alsopossible. In some embodiments, the first layer contains 100% syntheticfibers. In other embodiments, the first layer contains 0% syntheticfibers.

In some embodiments, in which bicomponent fibers are included in thefirst layer, the weight percentage of bicomponent fibers in the firstlayer may be greater than or equal to about 1%, greater than or equal toabout 20%, greater than or equal to about 40%, greater than or equal toabout 60%, greater than or equal to about 80%, greater than or equal toabout 90%, or greater than or equal to about 95%. In some instances, theweight percentage of bicomponent fibers in the first layer may be lessthan or equal to about 100%, less than or equal to about 98%, less thanor equal to about 85%, less than or equal to about 75%, less than orequal to about 50%, less than or equal to about 10%, less than or equalto about 5%, or less than or equal to about 3%. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 80% and less than or equal to about 100%). Other values ofweight percentage of bicomponent fibers in the first layer are alsopossible. In some embodiments, the first layer contains 100% bicomponentfibers. In other embodiments, the first layer contains 0% bicomponentfibers.

In some embodiments, in which cellulose fibers are included in the firstlayer, the weight percentage of cellulose fibers in the first layer maybe greater than or equal to about 1%, greater than or equal to about10%, greater than or equal to about 25%, greater than or equal to about50%, greater than or equal to about 75%, or greater than or equal toabout 90%. In some instances, the weight percentage of cellulose fibersin the first layer may be less than or equal to about 100%, less than orequal to about 70%, less than or equal to about 50%, less than or equalto about 30%, less than or equal to about 15%, or less than or equal toabout 5%. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 1% and less than or equal to about5%). Other values of weight percentage of cellulose fibers in the firstlayer are also possible. In some embodiments, the first layer contains100% cellulose fibers. In other embodiments, the first layer contains 0%cellulose fibers.

In some embodiments, in which fibrillated fibers are included in thefirst layer, the weight percentage of fibrillated fibers in the firstlayer may be greater than or equal to about 1%, greater than or equal toabout 10%, greater than or equal to about 25%, greater than or equal toabout 50%, greater than or equal to about 75%, or greater than or equalto about 90%. In some instances, the weight percentage of fibrillatedfibers in the first layer may be less than or equal to about 100%, lessthan or equal to about 70%, less than or equal to about 50%, less thanor equal to about 30%, less than or equal to about 10%, or less than orequal to about 2%. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 1% and less than or equalto about 10%). Other values of weight percentage of the fibrillatedfibers in the first layer are also possible. In some embodiments, thefirst layer contains 100% fibrillated fibers. In other embodiments, thefirst layer contains 0% fibrillated fibers.

In some embodiments, in which glass fibers are included in the firstlayer, the weight percentage of glass fibers (e.g., microglass fibers,chopped strand glass fibers, or a combination thereof) in the firstlayer may be greater than or equal to about 1%, greater than or equal toabout 10%, greater than or equal to about 25%, greater than or equal toabout 50%, greater than or equal to about 75%, or greater than or equalto about 90%. In some instances, the weight percentage of glass fibersin the first layer may be less than or equal to about 100%, less than orequal to about 70%, less than or equal to about 50%, less than or equalto about 30%, less than or equal to about 10%, or less than or equal toabout 2%. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 1% and less than or equal to about10%). Other values of weight percentage of the glass fibers in the firstlayer are also possible. In some embodiments, the first layer contains100% glass fibers. In other embodiments, the first layer contains 0%glass fibers.

Regardless of the type of fibers used to form the first layer, in someembodiments, the average diameter of the fibers of the first layer maybe, for example, greater than or equal to about 1 micron, greater thanor equal to about 3 microns, greater than or equal to about 5 microns,greater than or equal to about 8 microns, greater than or equal to about10 microns, greater than or equal to about 12 microns, greater than orequal to about 15 microns, greater than or equal to about 20 microns,greater than or equal to about 30 microns, or greater than or equal toabout 40 microns. In some instances, the fibers of the first layer mayhave an average diameter of less than or equal to about 50 microns, lessthan or equal to about 40 microns, less than or equal to about 30microns, less than or equal to about 20 microns, less than or equal toabout 15 microns, less than or equal to about 10 microns, less than orequal to about 7 microns, less than or equal to about 5 microns, or lessthan or equal to about 2 microns. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to about 1 micronand less than or equal to about 5 microns). Other values of averagefiber diameter are also possible.

In certain embodiments, the first layer may include a single layer. Inother embodiments, however, a first layer may include more than onelayer (i.e., sub-layers) to form a multi-layered structure. When a layerincludes more than one sub-layer, the plurality of sub-layers may differbased on certain features such as resistance and/or gradient structure.In certain cases, the plurality of sub-layers may be discrete andcombined by any suitable method, such as lamination, point bonding, orcollating. In some embodiments, the sub-layers are substantially joinedto one another (e.g., by lamination, point bonding. thermo-dot bonding,ultrasonic bonding, calendering, use of adhesives (e.g., glue-web),and/or co-pleating).

In other cases, sub-layers may be formed as a composite layer (e.g., bya wet laid process) or a multi-layer gradient structure. In one exampleof a first layer including sub-layers, a sub-layer including a pluralityof synthetic fibers may be combined with a sub-layer including glassfibers. In another example, a first layer may include a plurality ofsub-layers (e.g., three sub-layers), each sub-layer including meltblownsynthetic fibers. In some cases, each layer includes meltblown syntheticfibers having an average diameter of greater than or equal to 1 micron.Other values of average diameter are also possible, as described herein.Each of the sub-layers of the first layer may have any suitable basisweight and/or thickness, such as those basis weights and thicknessesdescribed herein for the first layer. Additionally, each of thesub-layers of the first layer may have performance characteristics(e.g., dust holding capacity, air permeability, and pressure drop) ofthose described herein for the first layer. The number of sub-layerswithin the first layer may be selected as desired. For instance, in someembodiments, the first layer may include, 1, 2, 3, 4, 5, etc. sub-layer.Other values for the number of sub-layers in the first layer are alsopossible.

A gradient across a layer (or across sub-layers) of a filter media mayinclude a change in one or more properties such as fiber diameter, fibertype, fiber composition, fiber length, fiber surface chemistry, poresize, material density, basis weight, a proportion of a component (e.g.,a binder, resin, crosslinker), and strength across a portion, or all of,a thickness of the layer or sub-layers. A layer (or sub-layers) mayoptionally include a gradient in one or more performance characteristicssuch as efficiency, dust holding capacity, pressure drop, and airpermeability across the thickness of the layer (or sub-layers).

Different types and configurations of gradients are possible within alayer (or sub-layers). In some embodiments, a gradient in one or moreproperties is gradual (e.g., linear, curvilinear) between a top surfaceand a bottom surface of the layer (or sub-layers). For example, a layer(or sub-layers) may have an increasing basis weight from the top surfaceto the bottom surface of the layer (or sub-layers). In anotherembodiment, a layer (or sub-layers) may include a step gradient in onemore properties across the thickness of the layer (or sub-layers). Inone such embodiment, the transition in the property may occur primarilyat an interface between two layers (or sub-layers). For example, afilter media, e.g., having a first layer (or sub-layer) including afirst fiber type and a second layer (or sub-layer) including a secondfiber type, may have an abrupt transition between fiber types across theinterface. In other words, each of the layers (or sub-layers) of thefiber web may be relatively distinct. In other embodiments, a gradientis characterized by a type of function across the thickness of the layer(or sub-layers). For example a gradient may be characterized by a sinefunction, a quadratic function, a periodic function, an aperiodicfunction, a continuous function, or a logarithmic function across thelayer (or sub-layers). Other types of gradients are also possible.

In some embodiments, the first layer (e.g., a capacity layer) may be acertain weight percentage of the entire filter media. In general, thefirst layer may be any suitable weight percentage of the entire filtermedia. For instance, in some embodiments, the weight percentage of thefirst layer in the entire filter media may be greater than or equal toabout 5%, greater than or equal to about 10%, greater than or equal toabout 20%, greater than or equal to about 30%, greater than or equal toabout 40%, greater than or equal to about 50%, greater than or equal toabout 60%, or greater than or equal to about 70%. In some instances, theweight percentage of the first layer in the entire filter media may beless than or equal to about 80%, less than or equal to about 60%, lessthan or equal to about 50%, less than or equal to about 40%, less thanor equal to about 30%, less than or equal to about 20%, or less than orequal to about 10%. Combinations of the above-referenced ranges are alsopossible (e.g., a weight percentage of greater than or equal to about10% and less than or equal to about 30%). Other values of weightpercentage of the first layer in the entire filter media are alsopossible.

The first layer (e.g., a capacity layer), as described herein, may havecertain structural characteristics, such as basis weight and thickness.For instance, in some embodiments, the first layer may have a basisweight of greater than or equal to about 30 g/m², greater than or equalto about 60 g/m², greater than or equal to about 70 g/m², greater thanor equal to about 90 g/m², greater than or equal to about 120 g/m²,greater than or equal to about 150 g/m², or greater than or equal toabout 180 g/m². In some instances, the first layer may have a basisweight of less than or equal to about 200 g/m², less than or equal toabout 150 g/m², less than or equal to about 90 g/m², less than or equalto about 70 g/m², less than or equal to about 60 g/m², or less than orequal to about 40 g/m². Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to about 60 g/m² and lessthan or equal to about 90 g/m²). Other values of basis weight are alsopossible. The basis weight may be determined according to the standardISO 536.

The thickness of the first layer may be selected as desired. Forinstance, in some embodiments, the first layer may have a thickness ofgreater than or equal to about 0.2 mm, greater than or equal to about0.5 mm, greater than or equal to about 0.8 mm, greater than or equal toabout 1 mm, greater than or equal to about 1.2 mm, greater than or equalto about 1.5 mm, or greater than or equal to about 1.8 mm. In someinstances, the first layer may have a thickness of less than or equal toabout 2.0 mm, less than or equal to about 1.6 mm, less than or equal toabout 1.2 mm, less than or equal to about 0.9 mm, less than or equal toabout 0.6 mm, or less than or equal to about 0.4 mm. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 0.5 mm and less than or equal to about 0.9 mm). Other values ofaverage thickness are also possible. The thickness may be determinedaccording to the standard ISO 534 at 2 N/m².

In some embodiments, the first layer may have a mean flow pore size ofgreater than or equal to about 30 microns, greater than or equal toabout 40 microns, greater than or equal to about 50 microns, greaterthan or equal to about 60 microns, greater than or equal to about 70microns, greater than or equal to about 80 microns, or greater than orequal to about 90 microns. In some instances, the first layer may havean average mean flow pore size of less than or equal to about 100microns, less than or equal to about 90 microns, less than or equal toabout 80 microns, less than or equal to about 70 microns, less than orequal to about 60 microns, less than or equal to about 50 microns, orless than or equal to about 40 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 40 microns and less than or equal to about 90 microns). Othervalues of average mean flow pore size are also possible. The mean flowpore size may be determined according to the standard ASTM E1294 (2008)(M.F.P.). In some embodiments, the first layer may have a larger meanflow pore size than that of the second layer.

The first layer, as described herein, may have advantageous performanceproperties, including dust holding capacity, air permeability, andpressure drop. For instance, in some embodiments, the first layer (e.g.,a capacity layer) may have a relatively high dust holding capacity. Forinstance, in some embodiments, the first layer may have a dust holdingcapacity of greater than or equal to about 5 g/m², greater than or equalto about 30 g/m², greater than or equal to about 50 g/m², greater thanor equal to about 70 g/m², greater than or equal to about 90 g/m²,greater than or equal to about 110 g/m², greater than or equal to about150 g/m², greater than or equal to about 200 g/m², or greater than orequal to about 250 g/m², greater than or equal to about 300 g/m², orgreater than or equal to about 350 g/m². In some instances, the capacitylayer may have a dust holding capacity of less than or equal to about400 g/m², less than or equal to about 300 g/m², less than or equal toabout 200 g/m², less than or equal to about 100 g/m², or less than orequal to about 80 g/m². Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to about 30 g/m² and lessthan or equal to about 100 g/m²). The dust holding capacity may bedetermined according to standard ISO 19438.

In some embodiments, the first layer may have an air permeability higherthan an air permeability of another layer in the filter media. In oneexample, the first layer (e.g., a capacity layer) may have an airpermeability higher than that of the second layer (e.g., efficiencylayer). For instance, in some embodiments, the first layer may have anair permeability of greater than or equal to about 100 L/m²sec, greaterthan or equal to about 150 L/m²sec, greater than or equal to about 350L/m²sec, greater than or equal to about 550 L/m²sec, greater than orequal to about 750 L/m²sec, greater than or equal to about 1000 L/m²sec,greater than or equal to about 1500 L/m²sec, or greater than or equal toabout 1700 L/m²sec. In some instances, the first layer may have an airpermeability of less than or equal to about 2000 L/m²sec, less than orequal to about 1600 L/m²sec, less than or equal to about 1200 L/m²sec,less than or equal to about 900 L/m²sec, less than or equal to about 650L/m²sec, less than or equal to about 400 L/m²sec, or less than or equalto about 200 L/m²sec. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to about 150 L/m²sec and lessthan or equal to about 900 L/m²sec). Other values of air permeabilityare also possible. The air permeability may be determined according tostandard EN/ISO 9327 (where the measurement area is 20 cm² at a 2 mbardifferential pressure).

The pressure drop of the first layer may be selected as desired. Forinstance, in some embodiments, the first layer may have a pressure dropof greater than or equal to about 5 Pa, greater than or equal to about15 Pa, greater than or equal to about 25 Pa, greater than or equal toabout 35 Pa, greater than or equal to about 45 Pa, greater than or equalto about 65 Pa, or greater than or equal to about 85 Pa. In someinstances, the first layer may have a pressure drop of less than orequal to about 100 Pa, less than or equal to about 75 Pa, less than orequal to about 50 Pa, less than or equal to about 40 Pa, less than orequal to about 30 Pa, or less than or equal to about 10 Pa. Combinationsof the above-referenced ranges are also possible (e.g., greater than orequal to about 15 Pa and less than or equal to about 50 Pa). Othervalues of pressure drop are also possible. The pressure drop, asdescribed herein, can be determined at 10.5 FPM face velocity using aTSI 8130 filtration tester.

As described herein, in some embodiments, the first layer (e.g.,capacity layer) may include synthetic fibers with an average fiberdiameter of greater than or equal to about 1 micron (e.g., greater thanor equal to 1 micron and less than or equal to about 5 microns). In someembodiments in which the first layer includes synthetic fibers, thesynthetic fibers may be formed by a meltblown process or a centrifugalspinning process, and may have a continuous length. In some cases, thefirst layer may include more than one sub-layer (e.g., 2-5 sub-layers).For example, the first layer may include three sub-layers and eachsub-layer may include synthetic fibers formed by a meltblown process ora centrifugal spinning process. In some cases, each sub-layer in thefirst layer may include a relatively high weight percentage of syntheticfibers (e.g., greater than or equal to about 70 wt %, greater than orequal to about 95 wt % synthetic fibers). Each sub-layer may contain,for instance, 100 wt % of synthetic fibers. The sub-layers in the firstlayer may be arranged to produce a gradient in a particular property(e.g., fiber diameter) across the first layer, as described herein. Thefirst layer may have a basis weight of, for example, greater than orequal to about 30 g/m² and less than or equal to about 150 g/m² (e.g.,greater than or equal to about 60 g/m² and less than or equal to about90 g/m²) and a thickness of, for example, greater than equal to about0.3 mm and less than or equal to about 1.5 mm (e.g., greater than equalto about 0.5 mm and less than or equal to about 0.9 mm). In some cases,the first layer may have a mean flow pore size of greater than or equalto about 70 microns; for example, greater than or equal to about 80microns and less than or equal to about 90 microns. In some cases, thefirst layer may have an air permeability of, for example, greater thanor equal to about 150 L/m²sec and less than or equal to about 900L/m²sec. In some instances, the first layer may have a higher mean flowpore size and/or a higher air permeability than those of the secondlayer.

As noted above, the filter media may include a second layer. In someembodiments, the second layer functions to enhance particle captureefficiency of the filter media, and may be referred to as an efficiencylayer. Typically, the efficiency layer does not include a spacer layer(e.g., spun-bond layer) when referring to the structural and performancecharacteristics of the efficiency layer, and/or the number of layerswithin the efficiency layer.

In some embodiments, the second layer may include more than one type offiber. For example, in certain embodiments, the second layer may includeone or more of a synthetic fiber, a bicomponent fiber, a cellulose fiber(e.g., regenerated, Lyocell, etc.), fibrillated fiber, and/or a glassfiber as described herein.

In some embodiments, in which synthetic fibers are included in thesecond layer, the weight percentage of synthetic fibers in the secondlayer may be greater than or equal to about 1%, greater than or equal toabout 20%, greater than or equal to about 40%, greater than or equal toabout 60%, greater than or equal to about 80%, greater than or equal toabout 90%, or greater than or equal to about 95%. In some instances, theweight percentage of synthetic fibers in the second layer may be lessthan or equal to about 100%, less than or equal to about 98%, less thanor equal to about 85%, less than or equal to about 75%, less than orequal to about 50%, or less than or equal to about 10%. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to about 80% and less than or equal to about 100%). Other valuesof weight percentage of synthetic fibers in the second layer are alsopossible. In some embodiments, the second layer includes 100% syntheticfibers. In other embodiments, the second layer may include 0% syntheticfibers.

In some embodiments, in which bicomponent fibers are included in thesecond layer, the second layer may optionally include bicomponentfibers. For instance, in some embodiments, the weight percentage ofbicomponent fibers in the second layer may be, for example, greater thanor equal to about 1%, greater than or equal to about 10%, greater thanor equal to about 25%, greater than or equal to about 50%, or greaterthan or equal to about 75%. In some instances, the weight percentage ofbicomponent fibers in the second efficiency layer may be less than orequal to about 100%, less than or equal to about 75%, less than or equalto about 50%, less than or equal to about 25%, less than or equal toabout 5%, or less than or equal to about 2%. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 1% and less than or equal to about 10%). Other values of weightpercentage of the bicomponent fibers in the second layer are alsopossible. In some embodiments, the second layer includes 100%bicomponent fibers. In other embodiments, the second layer may include0% bicomponent fibers.

In certain embodiments, the second layer may optionally includecellulose fibers, such as regenerated cellulose (e.g., rayon, Lyocell),fibrillated synthetic fibers, microfibrillated cellulose, natural fibers(e.g., hardwood, softwood), etc. For instance, in some embodiments, theweight percentage of cellulose fibers in the second layer may be greaterthan or equal to about 1%, greater than or equal to about 5%, greaterthan or equal to about 10%, greater than or equal to about 15%, greaterthan or equal to about 45%, greater than or equal to about 65%, orgreater than or equal to about 90%. In some instances, the weightpercentage of the cellulose fibers in the second layer may be less thanor equal to about 100%, less than or equal to about 85%, less than orequal to about 55%, less than or equal to about 20%, less than or equalto about 10%, or less than or equal to about 2%. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 1% and less than or equal to about 20%). Other values of weightpercentage of the cellulose fibers in the second layer are alsopossible. In some embodiments, the second layer includes 100% cellulosefibers. In other embodiments, the second layer may include 0% cellulosefibers.

In certain embodiments, the second layer may optionally includefibrillated fibers, such as fibrillated regenerated cellulose (e.g.,rayon, Lyocell), microfibrillated cellulose, fibrillated syntheticfibers, fibrillated natural fibers (e.g., hardwood, softwood), etc. Forinstance, in some embodiments, the weight percentage of fibrillatedfibers in the second layer may be greater than or equal to about 1%,greater than or equal to about 5%, greater than or equal to about 10%,greater than or equal to about 15%, greater than or equal to about 45%,greater than or equal to about 65%, or greater than or equal to about90%. In some instances, the weight percentage of the fibrillated fibersin the second layer may be less than or equal to about 100%, less thanor equal to about 85%, less than or equal to about 55%, less than orequal to about 20%, less than or equal to about 10%, or less than orequal to about 2%. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 1% and less than or equalto about 20%). Other values of weight percentage of the fibrillatedfibers in the second layer are also possible. In some embodiments, thesecond layer includes 100% fibrillated fibers. In other embodiments, thesecond layer may include 0% fibrillated fibers.

In other embodiments, the second layer may optionally include glassfibers (e.g., microglass and/or chopped glass fibers). For instance, insome embodiments, the weight percentage of the glass fibers in thesecond layer may be, for example, greater than or equal to about 0%,greater than or equal to about 10%, greater than or equal to about 25%,greater than or equal to about 50%, or greater than or equal to about75%. In some instances, the weight percentage of the glass fibers in thesecond layer may be less than or equal to about 100%, less than or equalto about 75%, less than or equal to about 50%, less than or equal toabout 25%, less than or equal to about 5%, or less than or equal toabout 2%. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 0% and less than or equal to about2%). Other values of weight percentage of the glass in the second layerare also possible. In some embodiments, the second layer includes 100%glass fibers. In other embodiments, the second layer may include 0%glass fibers.

Regardless of the type of fiber used to form the second layer, in someembodiments, the average diameter of the fibers of the second layer maybe relatively small. In some cases, the second layer includes nanofibersand/or microfibers. For instance, the plurality of fibers in the secondlayer may have an average diameter of, for example, less than or equalto about 1.5 microns, less than or equal to about 1.2 microns, less thanor equal to about 1.0 microns, less than or equal to about 0.8 microns,less than or equal to about 0.6 microns, less than or equal to about 0.4microns, or less than or equal to about 0.2 microns. In certainembodiments, the fibers of the second layer may have an average diameterof greater than or equal to about 0.1 microns, greater than or equal toabout 0.3 microns, greater than or equal to about 0.5 microns, orgreater than or equal to about 0.8 microns. Combinations of theabove-referenced ranges are also possible (e.g., less than or equal toabout 0.5 microns and greater than or equal to about 0.2 microns). Othervalues of average fiber diameter are also possible.

In other embodiments, the second layer may include a mixture of fibershaving an average fiber diameter of less than or equal to 1.5 microns,and larger, micron-sized fibers (e.g., fibrillated fibers). In suchembodiments, the average diameter of the fibers of the second layer maybe, for example, less than or equal to about 50 microns, less than orequal to about 40 microns, less than or equal to about 30 microns, lessthan or equal to about 20 microns, or less than or equal to about 10microns. In certain embodiments, the fibers of the second layer may havean average diameter of greater than or equal to about 1.5 microns,greater than or equal to about 5 microns, greater than or equal to about10 microns, greater than or equal to about 20 microns, greater than orequal to about 30 microns, or greater than or equal to about 40 microns.Combinations of the above-referenced ranges are also possible (e.g.,less than or equal to about 10 microns and greater than or equal toabout 1.5 microns). Other values of average fiber diameter are alsopossible.

In some embodiments, the fibers in the second layer may also have anaverage length which may depend on the method of formation of thefibers. For instance, in some embodiments, fibers formed by a melt-blownprocess may be continuous.

In certain embodiments, the second layer (e.g., an efficiency layer) mayinclude a single layer. In other embodiments, however, a second layermay include more than one layer (i.e., sub-layers) to form amulti-layered structure. When a layer includes more than one sub-layer,the plurality of sub-layers may differ based on certain features such asair permeability, basis weight, fiber type, efficiency, and/orcalendered design. In certain cases, the plurality of sub-layers may bediscrete and combined by any suitable method, such as lamination, pointbonding, or collating. In some embodiments, the sub-layers aresubstantially joined to one another (e.g., by lamination, point bonding.thermo-dot bonding, ultrasonic bonding, calendering, use of adhesives(e.g., glue-web), and/or co-pleating). In some cases, sub-layers may beformed as a composite layer (e.g., by a wet laid process).

In one example of a second layer (e.g., an efficiency layer) includingsub-layers, a sub-layer including a plurality of synthetic fibers may becombined with (e.g., positioned on top of) a sub-layer including glassfibers. In another example, a sub-layer including cellulose fibers(e.g., Lyocell fibers) may be combined with a sub-layer includingsynthetic fibers (e.g., a polybutylene terephthalate). In someembodiments, the second layer may be formed by a plurality of sub-layersincluding synthetic nanofibers and may optionally include a spun-bondlayer. Each of the sub-layers of the second layer may have any suitablebasis weight and/or thickness, such as those basis weights andthicknesses described herein for the first layer. Additionally, each ofthe sub-layers of the second layer may have performance characteristics(e.g., dust holding capacity, air permeability, and pressure drop) ofthose described herein for the first layer. The number of sub-layerswithin the second layer may be selected as desired. For instance, insome embodiments, the second layer may include, 1, 2, 3, 4, 5, 6, etc.sub-layers. Other values for the number of sub-layers in the secondlayer are also possible.

In general, the second layer (e.g., an efficiency layer) may be anysuitable weight percentage of the entire filter media. For instance, insome embodiments, the weight percentage of the second layer in theentire filter media may be greater than or equal to about 2%, greaterthan or equal to about 10%, greater than or equal to about 15%, greaterthan or equal to about 20%, greater than or equal to about 25%, greaterthan or equal to about 30%, greater than or equal to about 40%, orgreater than or equal to about 50%. In some instances, the weightpercentage of the second layer in the entire filter media may be lessthan or equal to about 60%, less than or equal to about 50%, less thanor equal to about 40%, less than or equal to about 30%, less than orequal to about 20%, less than or equal to about 15%, or less than orequal to about 5%. Combinations of the above-referenced ranges are alsopossible (e.g., a weight percentage of greater than or equal to about10% and less than or equal to about 30%). Other values of weightpercentage of the second layer in the entire filter media are alsopossible.

The second layer (e.g., an efficiency layer), as described herein, mayhave certain structural characteristics such as basis weight and meanpore flow size. For instance, in some embodiments, the second layer mayhave a basis weight of greater than or equal to about 0.5 g/m², greaterthan or equal to about 5 g/m², greater than or equal to about 15 g/m²,greater than or equal to about 20 g/m², greater than or equal to about30 g/m², greater than or equal to about 40 g/m², greater than or equalto about 50 g/m², greater than or equal to about 60 g/m², or greaterthan or equal to about 70 g/m². In some instances, the second layer mayhave a basis weight of less than or equal to about 100 g/m², less thanor equal to about 80 g/m², less than or equal to about 60 g/m², lessthan or equal to about 50 g/m², less than or equal to about 40 g/m²,less than or equal to about 30 g/m², less than or equal to about 25g/m², less than or equal to about 20 g/m², less than or equal to about10 g/m², or less than or equal to about 5 g/m². Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 10 g/m² and less than or equal to about 25 g/m²). Other valuesof basis weight are also possible. The basis weight may be determinedaccording to the standard ISO 536.

The mean flow pore size may be selected as desired. For instance, insome embodiments, the second layer may have an average mean flow poresize of greater than or equal to about 1 microns, greater than or equalto about 3 microns, greater than or equal to about 4 microns, greaterthan or equal to about 5 microns, greater than or equal to about 6microns, greater than or equal to about 7 microns, or greater than orequal to about 9 microns. In some instances, the second layer may havean average mean flow pore size of less than or equal to about 10microns, less than or equal to about 8 microns, less than or equal toabout 6 microns, less than or equal to about 5 microns, less than orequal to about 4 microns, or less than or equal to about 2 microns.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 3 microns and less than or equal to about6 microns). Other values of average mean flow pore size are alsopossible. The mean flow pore size may be determined according to thestandard ASTM E1294 (2008) (M.F.P.). In some embodiments, the secondlayer may have a mean flow pore size that is smaller than the mean flowpore sizes of the first and third layers.

The second layer (e.g., efficiency layer), as described herein, may haveadvantageous performance properties, including efficiency, airpermeability, pressure drop, and dust holding capacity. In someembodiments, the second layer may have a relatively high efficiency. Forinstance, in some embodiments, the efficiency of the second layer may begreater than or equal to about 80%, greater than or equal to about 90%,greater than or equal to about 95%, greater than or equal to about 96%,greater than or equal to about 97 greater than or equal to about 98,greater than or equal to about 99%, or greater than or equal to about99.9%. In some instances, the efficiency of the second layer may be lessthan or equal to about 99.99%, less than or equal to about 98%, lessthan or equal to about 97%, less than or equal to about 96%, or lessthan or equal to about 90%. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to about 80% and lessthan or equal to about 99.99%). Other values of the efficiency of thesecond layer are also possible. The efficiency may be determinedaccording to standard ISO 19438. As described in more detail below,efficiency can be measured at different particle sizes (e.g., for xmicron or greater particles, where x is described below), and the aboveranges of efficiency may be suitable for the various particle sizesdescribed herein. In some embodiments, x is 4 microns such that theabove ranges of efficiency are suitable for filtering out 4 micron orlarger particles.

In some embodiments, the second layer may have an air permeability lowerthan that of another layer in the filter media; for example, the airpermeability of the second layer may be lower than that of the firstand/or third layers. For instance, in some embodiments, the second layermay have an air permeability of less than or equal to about 500 L/m²sec,less than or equal to about 300 L/m²sec, less than or equal to about 125L/m²sec, less than or equal to about 110 L/m²sec, less than or equal toabout 90 L/m²sec, or less than or equal to about 65 L/m²sec. In someinstances, the second layer may have an air permeability of greater thanor equal to about 50 L/m²sec, greater than or equal to about 75 L/m²sec,greater than or equal to about 85 L/m²sec, greater than or equal toabout 95 L/m²sec, greater than or equal to about 115 L/m²sec, greaterthan or equal to about 200 L/m²sec, or greater than or equal to about300 L/m²sec. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 75 L/m²sec and less thanor equal to about 125 L/m²sec). Other values of air permeability arealso possible. The air permeability may be determined according tostandard EN/ISO 9327 (where the measurement area is 20 cm² at a 2 mbardifferential pressure).

The pressure drop of the second layer may be selected as desired. Forinstance, in some embodiments, the second layer may have a pressure dropof greater than or equal to about 25 Pa, greater than or equal to about60 Pa, greater than or equal to about 90 Pa, greater than or equal toabout 100 Pa, greater than or equal to about 110 Pa, greater than orequal to about 150 Pa, or greater than or equal to about 180 Pa. In someinstances, the second layer may have a pressure drop of less than orequal to about 200 Pa, less than or equal to about 165 Pa, less than orequal to about 140 Pa, less than or equal to about 120 Pa, less than orequal to about 105 Pa, less than or equal to about 75 Pa, or less thanor equal to about 40 Pa. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to about 90 Pa and less thanor equal to about 120 Pa). Other values of pressure drop are alsopossible. The pressure drop, as described herein, can be determined at10.5 FPM face velocity using a TSI 8130 filtration tester.

In some embodiments, the second layer may have a certain dust holdingcapacity. For instance, in some embodiments, the second layer may have adust holding capacity of greater than or equal to about 3 g/m², greaterthan or equal to about 10 g/m², greater than or equal to about 15 g/m²,greater than or equal to about 20 g/m², greater than or equal to about25 g/m², greater than or equal to about 30 g/m², or greater than orequal to about 35 g/m². In some instances, the second layer may have anair permeability of less than or equal to about 40 g/m², less than orequal to about 30 g/m², less than or equal to about 25 g/m², less thanor equal to about 20 g/m², less than or equal to about 15 g/m², lessthan or equal to about 10 g/m², or less than or equal to about 5 g/m².Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 15 g/m² and less than or equal to about30 g/m²). Other values of dust holding capacity are also possible. Thedust holding capacity may be determined according to standard ISO 19438.

As described herein, in some embodiments, the second layer (e.g.,efficiency layer) may include synthetic fibers with an average fiberdiameter of less than about or equal to about 1.5 microns (e.g., greaterthan or equal to about 0.2 microns and less than or equal to about 0.5microns, or greater than or equal to about 0.2 microns and less than orequal to about 1 micron). In some embodiments in which the first layerincludes synthetic fibers, the synthetic fibers may be formed by ameltblown process or a centrifugal spinning process, and may have acontinuous length. In some cases, the second layer may include more thanone sub-layer (e.g., 2-5 sub-layers). For example, the first layer mayinclude two sub-layers and each sub-layer may include synthetic fibersformed by a meltblown process or a centrifugal spinning process. In somecases, each sub-layer in the second layer may include a relatively highweight percentage of synthetic fibers (e.g., greater than or equal toabout 70 wt %, or greater than or equal to about 95 wt % syntheticfibers). In some embodiments, each sub-layer may contain 100 wt % ofsynthetic fibers. The sub-layers in the second layer may be arranged toproduce a gradient in a particular property (e.g., fiber diameter)across the second layer, as described herein. The second layer may havea basis weight of, for example, greater than or equal to about 10 g/m²and less than or equal to about 30 g/m² (e.g., greater than or equal toabout 15 g/m² and less than or equal to about 20 g/m²). In embodimentsin which the first layer includes sub-layers, each sub-layer may have abasis weight within these ranges. In some cases, the second layer mayhave a mean flow pore size of greater than or equal to about 1 micronand less than or equal to about 10 microns. In some embodiments, thesecond layer may have an air permeability of greater than or equal toabout 75 L/m²sec and less than or equal to about 125 L/m²sec. In someinstances, the second layer may have a smaller mean flow pore sizeand/or a lower air permeability than those of the first and thirdlayers. The second layer may optionally be joined to a fourth layer(e.g., a spun-bond layer), such that the second and fourth layers arebetween the first and third layers.

As described herein, a filter media may include a first, a second, athird, and a fourth layer. In some embodiments, the fourth layer may bea spacer layer adjacent to a second layer (e.g., an efficiency layer).In some cases, the fourth layer may be positioned between the second andthird layers. In general, the fourth layer may be formed by any suitableprocess, such as a spun-bond process, a meltblown process, or acentrifugal spinning process. In some cases, staple fibers can be used.The fourth layer may be formed of any suitable material, such as asynthetic polymer (e.g., polypropylene, polybutylene terephthalate,polyester, polycarbonate, polyamide, polyaramid, polyimide,polyethylene, polyether ether ketone, polyolefin, nylon, acrylics,polyvinyl alcohol, and combinations thereof). In some instances,regenerated cellulose (e.g., lyocell, rayon) fibers can be used. In someembodiments, the synthetic fibers are organic polymer fibers. Syntheticfibers may also include multi-component fibers (i.e., fibers havingmultiple compositions such as bicomponent fibers). In some cases,synthetic fibers may include meltblown fibers or fibers formed by acentrifugal spinning process, which may be formed of polymers describedherein (e.g., polyester, polypropylene). Other processes and materialsused to form the spacer layer are also possible.

In some embodiments, the fourth layer may have a relatively low basisweight. For instance, in some embodiments, the fourth layer may have abasis weight of less than or equal to about 70 g/m², less than or equalto about 50 g/m², less than or equal to about 30 g/m², less than orequal to about 20 g/m², less than or equal to about 15 g/m², or lessthan or equal to about 10 g/m². In some instances, the fourth layer mayhave a basis weight of greater than or equal to about 5 g/m², greaterthan or equal to about 12 g/m², greater than or equal to about 20 g/m²,greater than or equal to about 45 g/m², or greater than or equal toabout 60 g/m². Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 12 g/m² and less than orequal to about 15 g/m²). Other values of basis weight are also possible.The basis weight may be determined according to the standard ISO 536.

The thickness of the fourth layer (e.g., a spacer layer) may be selectedas desired. For instance, in some embodiments, the fourth layer may havea thickness of less than or equal to about 1.0 mm, less than or equal toabout 0.9 mm, less than or equal to about 0.5 mm, less than or equal toabout 0.4 mm, less than or equal to about 0.3 mm, or less than or equalto about 0.2 mm. In some instances, the fourth layer may have athickness of greater than or equal to about 0.1 mm, greater than orequal to about 0.2 mm, greater than or equal to about 0.25 mm, greaterthan or equal to about 0.3 mm, greater than or equal to about 0.4 mm,greater than or equal to about 0.6 mm, or greater than or equal to about0.8 mm. Combinations of the above-referenced ranges are also possible(e.g., a thickness of greater than or equal to about 0.2 mm and lessthan or equal to about 0.3 mm). Other values of thickness are alsopossible. The thickness may be determined according to the standard ISO534.

In some embodiments, the fourth layer may have a relatively high airpermeability; for example, the air permeability of the fourth layer maybe higher than that of the first, second and/or third layers. Forinstance, in some embodiments, the fourth layer may have an airpermeability of greater than or equal to about 500 L/m²sec, greater thanor equal to about 700 L/m²sec, greater than or equal to about 1,000L/m²sec, greater than or equal to about 1,500 L/m²sec, greater than orequal to about 2,000 L/m²sec, greater than or equal to about 5,000L/m²sec, or greater than or equal to about 10,000 L/m²sec. In someembodiments, the air permeability of the fourth layer may be less thanor equal to about 12,000 L/m²sec, less than or equal to about 10,000L/m²sec, less than or equal to about 8,000 L/m²sec, less than or equalto about 5,000 L/m²sec, less than or equal to about 2,000 L/m²sec, orless than or equal to about 1,000 L/m²sec. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 1,000 L/m²sec and less than or equal to about 12,000 L/m²sec).Other values of air permeability are also possible. The air permeabilitymay be determined according to standard EN/ISO 9327 (where themeasurement area is 20 cm² at a 2 mbar differential pressure).

In certain embodiments in which the fourth layer is present, the fourthlayer may be formed by a spunbond process and may include a syntheticfiber, such as a fiber formed of polypropylene, polybutyleneterephthalate, or polyester. The fourth layer may have a basis weightof, for example, greater than or equal to about 5 g/m² and less than orequal to about 70 g/m², and a thickness of, for example, less than orequal to about 0.5 mm.

A filter media including a plurality of layers, as described herein, mayhave enhanced filtration properties (e.g., dust holding capacity,lifetime, etc.). In some embodiments, the order of the layers in thefilter media may influence the filtration properties of the filtermedia. In one example, the filter media may include a first, a second,and a third layer in numerical order (i.e., the second layer may bepositioned between the first and third layers), such that the airpermeability of the second layer may be lower than the air permeabilityof the first and third layers. The air permeability across the filtermedia may be described as having an hourglass configuration (i.e., theair permeability of a middle layer of the filter media may be lower thana layer upstream and a layer downstream with respect to the middlelayer). In some instances, a filter media having an air permeability inthis configuration may have enhanced filtration properties compared tocertain existing filter media, in which the air permeability decreasesacross the media from an upstream side to a downstream side or from adownstream side to an upstream side. It should be appreciated that sucha configuration of layers may be formed by any suitable number orarrangement of layers (e.g., four layers in non-numerical order).

In certain embodiments, an hourglass configuration may be formed withmean flow pore size (i.e., the mean flow pore size of a middle layer ofthe filter media may be lower than a layer upstream and a layerdownstream with respect to the middle layer). For example, the secondlayer (e.g., efficiency layer) may have a mean flow pore size that issmaller than the mean flow pore sizes of the first and third layers(e.g., capacity and support layers, respectively). It should beappreciated that such a configuration of layers may be formed by anysuitable number or arrangement of layers (e.g., four layers innon-numerical order).

In one set of embodiments, a filter media may include a first, a second,a third, and optionally a fourth layer. The second layer (and optionallythe fourth layer) may be positioned between the first and third layers.When present, the fourth layer may be positioned between the second andthird layers. The first layer (e.g., capacity layer) may includesynthetic fibers with an average fiber diameter of greater than or equalto about 1 micron (e.g., greater than or equal to 1 micron and less thanor equal to about 5 microns). In some embodiments in which the firstlayer includes synthetic fibers, the synthetic fibers may be formed by ameltblown process or a centrifugal spinning process, and may have acontinuous length. In some cases, the first layer may include more thanone sub-layer (e.g., 2-5 sub-layers). For example, the first layer mayinclude three sub-layers and each sub-layer may include synthetic fibersformed by a meltblown process or a centrifugal spinning process. In somecases, each sub-layer in the first layer may include a relatively highweight percentage of synthetic fibers (e.g., greater than or equal toabout 70 wt %, greater than or equal to about 95 wt % synthetic fibers).Each sub-layer may contain, for instance, 100 wt % of synthetic fibers.The sub-layers in the first layer may be arranged to produce a gradientin a particular property (e.g., fiber diameter) across the first layer,as described herein. The first layer may have a basis weight of, forexample, greater than or equal to about 30 g/m² and less than or equalto about 150 g/m² (e.g., greater than or equal to about 60 g/m² and lessthan or equal to about 90 g/m²) and a thickness of, for example, greaterthan equal to about 0.3 mm and less than or equal to about 1.5 mm (e.g.,greater than equal to about 0.5 mm and less than or equal to about 0.9mm). In some cases, the first layer may have a mean flow pore size of,for example, greater than or equal to 50 microns and less than or equalto 100 microns (e.g., greater than or equal to 70 microns and less thanor equal to 90 microns). In some cases, the first layer may have an airpermeability of, for example, greater than or equal to about 150 L/m²secand less than or equal to about 900 L/m²sec. In some instances, thefirst layer may have a higher mean flow pore size and/or a higher airpermeability than those of the second layer.

The second layer (e.g., efficiency layer) may include synthetic fiberswith an average fiber diameter of less than about or equal to about 1.5microns (e.g., greater than or equal to about 0.2 microns and less thanor equal to about 0.5 microns, or greater than or equal to about 0.2microns and less than or equal to about 1 micron). In some embodimentsin which the first layer includes synthetic fibers, the synthetic fibersmay be formed by a meltblown process or a centrifugal spinning process,and may have a continuous length. In some cases, the second layer mayinclude more than one sub-layer (e.g., 2-5 sub-layers). For example, thefirst layer may include two sub-layers and each sub-layer may includesynthetic fibers formed by a meltblown process or a centrifugal spinningprocess. In some cases, each sub-layer in the second layer may include arelatively high weight percentage of synthetic fibers (e.g., greaterthan or equal to about 70 wt %, or greater than or equal to about 95 wt% synthetic fibers). In some embodiments, each sub-layer may contain 100wt % of synthetic fibers. The sub-layers in the second layer may bearranged to produce a gradient in a particular property (e.g., fiberdiameter) across the second layer, as described herein. The second layermay have a basis weight of, for example, greater than or equal to about10 g/m² and less than or equal to about 30 g/m² (e.g., greater than orequal to about 15 g/m² and less than or equal to about 20 g/m²). Inembodiments in which the first layer includes sub-layers, each sub-layermay have a basis weight within these ranges. In some cases, the secondlayer may have a mean flow pore size of greater than or equal to about 1micron and less than or equal to about 10 microns. In some embodiments,the second layer may have an air permeability of greater than or equalto about 75 L/m²sec and less than or equal to about 125 L/m²sec. In someinstances, the second layer may have a smaller mean flow pore sizeand/or a lower air permeability than those of the first and thirdlayers. The second layer may optionally be joined to a fourth layer(e.g., a spun-bond layer), such that the second and fourth layers arebetween the first and third layers.

The third layer (e.g., support layer) may, in some embodiments, includecellulose fibers. The cellulose fibers may have an average diameter of,for example, greater than or equal to about 20 microns and less than orequal to about 50 microns (e.g., greater than or equal to about 30microns and less than or equal to about 40 microns), and an averagefiber length of, for example, greater than or equal to about 1 mm andless than or equal to about 10 mm. In some cases, the third layer mayinclude a relatively high weight percentage of cellulose fibers (e.g.,greater than or equal to about 70 wt %, or greater than or equal toabout 95 wt % cellulose fibers). In one embodiment, the third layer mayinclude 100 wt % cellulose fibers. The third layer may includeperforations in some embodiments, but do not include perforations inother embodiments. When perforations are present, the perforations maycover a certain percentage of the surface area of the layer. Forexample, the perforations may cover greater than or equal to about 5%and less than or equal to about 20% of the surface area of the layer.The perforations may have a periodicity of, for example, greater than orequal to about 5 mm and less than or equal to about 20 mm. The averagediameter of the perforations may be, for example, greater than or equalto about 0.5 mm and less than or equal to about 5 mm. In some instances,the third layer may be a single layer and may have a thickness ofgreater than or equal to about 0.1 mm and less than or equal to about0.5 mm (e.g., greater than or equal to about 0.2 mm and less than orequal to about 0.4 mm). The basis weight of the third layer may be, forexample, greater than or equal to about 75 g/m² and less than or equalto 150 g/m². The dry Mullen Burst strength of the third layer may be,for example, greater than or equal to about 100 kPa and less than orequal to about 500 kPa (e.g., greater than or equal to about 200 kPa andless than or equal to about 300 kPa). In some cases, the third layer mayhave a mean flow pore size of, for example, greater than or equal to 40microns and less than or equal to 70 microns. The air permeability ofthe third layer may be, for example, greater than or equal to about 400L/m²sec and less than or equal to about 1500 L/m²sec. In some instances,the third layer may have a higher mean flow pore size and/or a higherair permeability than those of the second layer, e.g., in someembodiments in which the second layer is positioned between the firstand third layers.

The filter media may optionally include a fourth layer joined to thesecond layer. In certain embodiments in which the fourth layer ispresent, the fourth layer may be formed by a spunbond process and mayinclude a synthetic fiber, such as a fiber formed of polypropylene,polybutylene terephthalate, or standard polyester. The fourth layer mayhave a basis weight of, for example, greater than or equal to about 5g/m² and less than or equal to about 70 g/m², and a thickness of, forexample, less than or equal to about 0.5 mm. Other configurations of thefirst, second, third, and fourth layers are also possible, as describedherein.

The filter media described herein may have certain structuralcharacteristics such as basis weight and dry Mullen Burst strength. Insome embodiments, the filter media may have a basis weight of greaterthan or equal to about 50 g/m², greater than or equal to about 100 g/m²,greater than or equal to about 150 g/m², greater than or equal to about200 g/m², greater than or equal to about 250 g/m², greater than or equalto about 350 g/m², or greater than or equal to about 425 g/m². In someinstances, the filter media may have a basis weight of less than orequal to about 500 g/m², less than or equal to about 400 g/m², less thanor equal to about 300 g/m², less than or equal to about 200 g/m², orless than or equal to about 100 g/m². Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 155 g/m² and less than or equal to about 285 g/m²). Othervalues of basis weight are also possible. The basis weight may bedetermined according to the standard ISO 536.

In some embodiments, the filter media may have a relatively high dryMullen Burst strength. The dry Mullen Burst strength may be, forexample, greater than or equal to about 100 kPa, greater than or equalto about 200 kPa, greater than or equal to about 250 kPa, greater thanor equal to about 300 kPa, greater than or equal to about 350 kPa,greater than or equal to about 400 kPa, greater than or equal to about450 kPa, or greater than or equal to about 500 kPa. In some instances,the filter media may have a dry Mullen Burst strength of less than orequal to about 600 kPa, less than or equal to about 500 kPa, less thanor equal to about 400 kPa, less than or equal to about 300 kPa, or lessthan or equal to about 200 kPa. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to about 100 kPaand less than or equal to about 500 kPa). Other values of dry MullenBurst strength are also possible. The dry Mullen Burst strength may bedetermined according to the standard DIN 53141.

In some embodiments, a filter media, as described herein, may have otheradvantageous properties. For example, in some embodiments, the filtermedia may be formed without including glass in the media. In otherembodiments, the filter media may contain a small amount of glass (e.g.,less than or equal to about 5 wt %, less than or equal to about 2 wt %,or less than or equal to about 1 wt %). While often having desirablefiltration performance, in certain applications filter media containingglass fibers may shed during handling, release sodium, releasemicrofibers, and/or have reduced manufacturability (e.g., pleating). Itshould be appreciated, however, that in other embodiments, the filtermedia described herein may include glass fibers in amounts higher than 5wt %.

In some cases, the filter media described herein may have an improvedlifetime. The lifetime, as referred to herein, is measured according tothe standard ISO 4020. The testing can be performed using mineral oil,4-6 cST at 23° C. as the test fluid, and carbon black and Mira 2aluminum oxide as the organic and inorganic contaminants, respectively.The flow rate of the test fluid is 36.7 Lpm/m² and the terminaldifferential pressure is a 70 kPa rise over the clean filter media. Thetest fixture may be an IBR FS housing with a 90 mm diameter and the flatsheet media samples can be cut to fit the 90 mm FS housing. Theinorganic challenge involves the use of 20 grams of Mira 2 aluminumoxide per 20 liters of mineral oil, 4-6 cST, and the organic challengeinvolves the use of 1.25 grams of carbon black per 20 liters of mineraloil, 4-6 cST. The lifetime is determined to be the time, in minutes,required to reach a terminal differential pressure of 70 kPa over theclean filter media with no contaminants.

In some embodiments, the filter media may have an average lifetime ofgreater than or equal to about 20 minutes, greater than or equal toabout 40 minutes, greater than or equal to about 55 minutes, greaterthan or equal to about 60 minutes, greater than or equal to about 70minutes, greater than or equal to about 85 minutes, greater than orequal to about 100 minutes, or greater than or equal to about 150minutes. In some instances, the filter media may have an averagelifetime of less than or equal to about 200 minutes, less than or equalto about 160 minutes, less than or equal to about 130 minutes, less thanor equal to about 110 minutes, less than or equal to about 85 minutes,or less than or equal to about 65 minutes. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 40 minutes and less than or equal to about 85 minutes). Othervalues of average lifetime are also possible. The lifetime may bedetermined according to the standard ISO 4020.

In certain cases, the filter media may have a relatively high dustholding capacity. For instance, in some embodiments, the filter mediamay have a dust holding capacity of greater than or equal to about 50g/m², greater than or equal to about 150 g/m², greater than or equal toabout 200 g/m², greater than or equal to about 250 g/m², greater than orequal to about 300 g/m², greater than or equal to about 350 g/m²,greater than or equal to about 400 g/m², or greater than or equal toabout 450 g/m². In some instances, the filter media may have a dustholding capacity of less than or equal to about 500 g/m², less than orequal to about 400 g/m², less than or equal to about 300 g/m², less thanor equal to about 200 g/m², or less than or equal to about 100 g/m².Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 250 g/m² and less than or equal to about400 g/m²). The dust holding capacity may be determined according tostandard ISO 19438.

In some embodiments, the filter media may be designed to have aparticular range of pressure drop. For instance, in some embodiments,the filter media may have a pressure drop of greater than or equal toabout 25 Pa, greater than or equal to about 60 Pa, greater than or equalto about 90 Pa, greater than or equal to about 100 Pa, greater than orequal to about 110 Pa, greater than or equal to about 150 Pa, or greaterthan or equal to about 180 Pa. In some instances, the filter media mayhave a pressure drop of less than or equal to about 200 Pa, less than orequal to about 165 Pa, less than or equal to about 140 Pa, less than orequal to about 120 Pa, less than or equal to about 105 Pa, less than orequal to about 75 Pa, or less than or equal to about 40 Pa. Combinationsof the above-referenced ranges are also possible (e.g., greater than orequal to about 25 Pa and less than or equal to about 120 Pa). Othervalues of pressure drop are also possible. The pressure drop, asdescribed herein, can be determined at 10.5 FPM face velocity using aTSI 8130 filtration tester.

In some embodiments, the filter media may have a certain airpermeability. For instance, in some embodiments, the filter media mayhave an air permeability of less than or equal to about 1000 L/m²sec,less than or equal to about 800 L/m²sec, less than or equal to about 600L/m²sec, less than or equal to about 400 L/m²sec, less than or equal toabout 100 L/m²sec, or less than or equal to about 50 L/m²sec. In someinstances, the filter media may have an air permeability of greater thanor equal to about 30 L/m²sec, greater than or equal to about 150L/m²sec, greater than or equal to about 250 L/m²sec, greater than orequal to about 500 L/m²sec, greater than or equal to about 750 L/m²sec,or greater than or equal to about 900 L/m²sec. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 75 L/m²sec and less than or equal to about 150 L/m²sec). Othervalues of air permeability are also possible. The air permeability maybe determined according to standard EN/ISO 9327 (A=20 cm² at a 2 mbardifferential pressure).

The filter media described herein may be used for the filtration ofvarious particle sizes. In a typical test for measuring efficiency of alayer or the entire media (e.g., according to the standard ISO 19438),particle counts (particles per milliliter) at the particle size, x,selected (e.g., where x is 1, 3, 4, 5, 7, 10, 15, 20, 25, or 30 microns)upstream and downstream of the layer or media can be taken at ten pointsequally divided over the time of the test. Generally, a particle size ofx means that x micron or greater particles will be captured by the layeror media. The average of upstream and downstream particle counts can betaken at the selected particle size. From the average particle countupstream (injected −C₀) and the average particle count downstream(passed thru −C) the filtration efficiency test value for the particlesize selected can be determined by the relationship [(100−[C/C₀])*100%].As described herein, efficiency can be measured according to standardISO 19328. A similar protocol can be used for measuring initialefficiency, which refers to the average efficiency measurements of themedia at 4, 5, and 6 minutes after running the test. Unless otherwiseindicated, efficiency and initial efficiency measurements describedherein refer to values where x=4 microns.

Efficiency can also be expressed in terms of a Beta value (or Betaratio), where Beta_((x))=y is the ratio of upstream count (C₀) todownstream count (C), and where x is the minimum particle size that willachieve the actual ratio of C₀ to C that is equal to y. The penetrationfraction of the media is 1 divided by the Beta_((x)) value (y), and theefficiency fraction is 1−penetration fraction. Accordingly, theefficiency of the media is 100 times the efficiency fraction, and100*(1−1/Beta_((x)))=efficiency percentage. For example, a filter mediahaving a Beta_((x))=200 has an efficiency of [1−( 1/200)]*100, or 99.5%for x micron or greater particles. The filter media described herein mayhave a wide range of Beta values, e.g., a Beta_((x))=y, where x can be,for example, 1, 3, 4, 5, 7, 10, 12, 15, 20, 25, 30, 50, 70, or 100, andwhere y can be, for example, 2, 10, 75, 100, 200, or 1000. It should beunderstood that other values of x and y are also possible; for instance,in some cases, y may be greater than 1000. It should also be understoodthat for any value of x, y may be any number (e.g., 10.2, 12.4)representing the actual ratio of C₀ to C. Likewise, for any value of y,x may be any number representing the minimum particle size that willachieve the actual ratio of C₀ to C that is equal to y. Unless otherwiseindicated, beta measurements described herein refer to values where x=4microns.

In some embodiments, the filter media may have a relatively highefficiency. For instance, in some embodiments, the efficiency of thefilter media may be greater than or equal to about 80%, greater than orequal to about 90%, greater than or equal to about 95%, greater than orequal to about 96%, greater than or equal to about 97%, greater than orequal to about 98%, greater than or equal to about 99%, or greater thanor equal to about 99.9%. In some instances, the efficiency of the filtermedia may be less than or equal to about 99.99%, less than or equal toabout 98%, less than or equal to about 97%, less than or equal to about96%, or less than or equal to about 90%. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 80% and less than or equal to about 99.99%). Other values ofthe efficiency of the filter media are also possible. The efficiency maybe determined according to standard ISO 19438. As described herein,efficiency can be measured at different particle sizes (e.g., for xmicron or greater particles, where x is described herein), and the aboveranges of efficiency may be suitable for the various particle sizesdescribed herein. In some embodiments, x is 4 microns such that theabove ranges of efficiency are suitable for filtering out 4 micron orlarger particles.

The filter media may also have a relatively high initial efficiency. Theinitial efficiency of the filter media may be greater than or equal toabout 80%, greater than or equal to about 90%, greater than or equal toabout 95%, greater than or equal to about 96%, greater than or equal toabout 97%, greater than or equal to about 98%, greater than or equal toabout 99%, or greater than or equal to about 99.9%. In some instances,the initial efficiency of the filter media may be less than or equal toabout 99.99%, less than or equal to about 98%, less than or equal toabout 97%, less than or equal to about 96%, or less than or equal toabout 90%. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 80% and less than or equal toabout 99.99%). Other values of the initial efficiency of the filtermedia are also possible. The initial efficiency may be determinedaccording to standard ISO 19438. As described herein, initial efficiencycan be measured at different particle sizes (e.g., for x micron orgreater particles, where x is described herein), and the above ranges ofinitial efficiency may be suitable for the various particle sizesdescribed herein. In some embodiments, x is 4 microns such that theabove ranges of initial efficiency are suitable for filtering out 4micron or larger particles.

In some embodiments, one or more layers of a filter media describedherein include a resin. Typically, a resin or any additional components,if present, are present in limited amounts. In some embodiments, one ormore layers may include wet and/or dry strength resins that include, forexample, natural polymers (starches, gums), cellulose derivatives, suchas carboxymethyl cellulose, methylcellulose, hemicelluloses, syntheticpolymers such as phenolics, latexes, polyamides, polyacrylamides,urea-formaldehyde, melamine-formaldehyde, polyamides), surfactants,coupling agents, crosslinking agents, and/or conductive additives,amongst others.

In some embodiments, a layer may include a binder resin. The binderresin is not in fiber form and is to be distinguished from binder fiber(e.g., multi-component fiber) described above. In general, the binderresin may have any suitable composition. For example, the binder resinmay comprise a thermoplastic (e.g., acrylic, polyvinylacetate,polyester, polyamide), a thermoset (e.g., epoxy, phenolic resin), or acombination thereof. In some cases, a binder resin includes one or moreof a vinyl acetate resin, an epoxy resin, a polyester resin, acopolyester resin, a polyvinyl alcohol resin, an acrylic resin such as astyrene acrylic resin, and a phenolic resin. Other resins are alsopossible.

The amount of binder resin in a layer (e.g., a first, second, third,and/or fourth layer) may vary. For instance, in some embodiments, theweight percentage of binder resin in the layer may be greater than orequal to about 2 wt %, greater than or equal to about 5 wt %, greaterthan or equal to about 10 wt %, greater than or equal to about 15 wt %,greater than or equal to about 20 wt %, greater than or equal to about25 wt %, greater than or equal to about 30 wt %, greater than or equalto about 35 wt %, or greater than or equal to about 40 wt %. In somecases, the weight percentage of binder resin in the layer may be lessthan or equal to about 45 wt %, less than or equal to about 40 wt %,less than or equal to about 35 wt %, less than or equal to about 30 wt%, less than or equal to about 25 wt %, less than or equal to about 20wt %, less than or equal to about 15 wt %, less than or equal to about10 wt %, or less than or equal to about 5 wt %. Combinations of theabove-referenced ranges are also possible (e.g., a weight percentage ofbinder resin of greater than or equal to about 5 wt % and less than orequal to about 35 wt %). Other ranges are also possible.

The amount of binder resin in the filter media may also vary. Forinstance, in some embodiments, the weight percentage of binder resin inthe filter media may be greater than or equal to about 2 wt %, greaterthan or equal to about 5 wt %, greater than or equal to about 10 wt %,greater than or equal to about 15 wt %, greater than or equal to about20 wt %, greater than or equal to about 25 wt %, greater than or equalto about 30 wt %, or greater than or equal to about 35 wt %. In somecases, the weight percentage of binder resin in the layer may be lessthan or equal to about 40 wt %, less than or equal to about 35 wt %,less than or equal to about 30 wt %, less than or equal to about 25 wt%, less than or equal to about 20 wt %, less than or equal to about 15wt %, less than or equal to about 10 wt %, or less than or equal toabout 5 wt %. Combinations of the above-referenced ranges are alsopossible (e.g., a weight percentage of binder resin of greater than orequal to about 5 wt % and less than or equal to about 35 wt %). Otherranges are also possible.

As described further below, the binder resin may be added to the fibersin any suitable manner including, for example, in the wet state. In someembodiments, the binder coats the fibers and is used to adhere fibers toeach other to facilitate adhesion between the fibers. Any suitablemethod and equipment may be used to coat the fibers, for example, usingcurtain coating, gravure coating, melt coating, dip coating, knife rollcoating, or spin coating, amongst others. In some embodiments, thebinder is precipitated when added to the fiber blend. When appropriate,any suitable precipitating agent (e.g., Epichlorohydrin, fluorocarbon)may be provided to the fibers, for example, by injection into the blend.In some embodiments, upon addition to the fiber blend, the binder resinis added in a manner such that the layer is impregnated with the binderresin (e.g., the binder resin permeates throughout the layer). In amulti-layered web, a binder resin may be added to each of the layersseparately prior to combining the layers, or the binder resin may beadded to the layer after combining the layers. In some embodiments,binder resin is added to the fiber blend while in a dry state, forexample, by spraying or saturation impregnation, or any of the abovemethods. In other embodiments, a binder resin is added to a wet layer.

In some embodiments, a binder resin may be added to a layer by a solventsaturation process. In certain embodiments, a polymeric material can beimpregnated into filter medium either during or after the filter mediumis being manufactured on a papermaking machine. For example, during amanufacturing process described herein, after the article containingfirst layer and second layer is formed and dried, a polymeric materialin a water based emulsion or an organic solvent based solution can beadhered to an application roll and then applied to the article under acontrolled pressure by using a size press or gravure saturator. Theamount of the polymeric material impregnated into the filter mediumtypically depends on the viscosity, solids content, and absorption rateof filter medium. As another example, after a layer is formed, it can beimpregnated with a polymeric material by using a reverse roll applicatorfollowing the just-mentioned method and/or by using a dip and squeezemethod (e.g., by dipping a dried filter media into a polymer emulsion orsolution and then squeezing out the excess polymer by using a nip). Apolymeric material can also be applied to a layer by other methods knownin the art, such as spraying or foaming.

Layers or sub-layers for incorporation into a filter media, as describedherein, may be produced using any suitable processes, such as using awet laid process (e.g., a process involving a pressure former, arotoformer, a fourdrinier, a hybrid former, or a twin wire process) or anon-wet laid process (e.g., a dry laid process, an air laid process, aspunbond process, a meltblown process, an electrospinning process, acentrifugal spinning process, or a carding process). In general, a wetlaid process involves mixing together of fibers of one or more type toprovide a fiber slurry. The slurry may be, for example, an aqueous-basedslurry. In certain embodiments, the various fibers are optionally storedseparately, or in combination, in various holding tanks prior to beingmixed together (e.g., to achieve a greater degree of uniformity in themixture).

For instance, a first fiber may be mixed and pulped together in onecontainer and a second fiber may be mixed and pulped in a separatecontainer. The first fibers and the second fibers may subsequently becombined together into a single fibrous mixture. Appropriate fibers maybe processed through a pulper before and/or after being mixed together.In some embodiments, combinations of fibers are processed through apulper and/or a holding tank prior to being mixed together. It can beappreciated that other components may also be introduced into themixture.

In certain embodiments, one or more layers described herein (e.g., afirst, a second, a third, and/or a fourth layer) may include amulti-layered structure that may be formed by a wet laid process. Forexample, a first dispersion (e.g., a pulp) containing fibers in asolvent (e.g., an aqueous solvent such as water) can be applied onto awire conveyor in a papermaking machine (e.g., a fourdrinier or arotoformer) to form first layer supported by the wire conveyor. A seconddispersion (e.g., another pulp) containing fibers in a solvent (e.g., anaqueous solvent such as water) may be applied onto the first layereither at the same time or subsequent to deposition of the first layeron the wire. Vacuum is continuously applied to the first and seconddispersions of fibers during the above process to remove the solventfrom the fibers, thereby resulting in an article containing first andsecond layers. The article thus formed may then be dried and, ifnecessary, further processed (e.g., calendered) by using known methodsto form multi-layered layers. In some embodiments, such a process mayresult in a gradient in at least one property across the thickness ofthe two or more layers, as described herein.

Any suitable method for creating a fiber slurry may be used. In someembodiments, further additives are added to the slurry to facilitateprocessing. The temperature may also be adjusted to a suitable range,for example, between 33° F. and 100° F. (e.g., between 50° F. and 85°F.). In some cases, the temperature of the slurry is maintained. In someinstances, the temperature is not actively adjusted.

In some embodiments, the wet laid process uses similar equipment as in aconventional papermaking process, for example, a hydropulper, a formeror a headbox, a dryer, and an optional converter. A layer can also bemade with a laboratory handsheet mold in some instances. As discussedabove, the slurry may be prepared in one or more pulpers. Afterappropriately mixing the slurry in a pulper, the slurry may be pumpedinto a headbox where the slurry may or may not be combined with otherslurries. Other additives may or may not be added. The slurry may alsobe diluted with additional water such that the final concentration offiber is in a suitable range, such as for example, between about 0.1% to0.5% by weight.

Wet laid processes may be particularly suitable for forming amulti-layered structure within a layer (e.g., a first, a second, athird, and/or a fourth layer), or for combining two or more such layers,as described herein. For instance, in some cases, the same slurry ispumped into separate headboxes to form different layers within a layer.For laboratory samples, a first layer can be formed from a fiber slurry,drained and dried and then a second layer can be formed on top from afiber slurry. In other embodiments, one layer can be formed and anotherlayer can be formed on top, drained, and dried.

In some cases, the pH of the fiber slurry may be adjusted as desired.For instance, fibers of the slurry may be dispersed under generallyneutral conditions.

Before the slurry is sent to a headbox, the slurry may optionally bepassed through centrifugal cleaners and/or pressure screens for removingunfiberized material. The slurry may or may not be passed throughadditional equipment such as refiners or deflakers to further enhancethe dispersion or fibrillation of the fibers. For example, deflakers maybe useful to smooth out or remove lumps or protrusions that may arise atany point during formation of the fiber slurry. Fibers may then becollected on to a screen or wire at an appropriate rate using anysuitable equipment, e.g., a fourdrinier, a rotoformer, a cylinder, or aninclined wire fourdrinier.

In some embodiments, the process involves introducing a binder (and/orother components) into a pre-formed fiber layer. In some embodiments, asthe fiber layer is passed along an appropriate screen or wire, differentcomponents included in the binder, which may be in the form of separateemulsions, are added to the fiber layer using a suitable technique. Insome cases, each component of the binder resin is mixed as an emulsionprior to being combined with the other components and/or fiber layer. Insome embodiments, the components included in the binder may be pulledthrough the fiber layer using, for example, gravity and/or vacuum. Insome embodiments, one or more of the components included in the binderresin may be diluted with softened water and pumped into the fiberlayer. In some embodiments, a binder may be introduced to the fiberlayer by spraying onto the formed media, or by any other suitablemethod, such as for example, size press application, foam saturation,curtain coating, rod coating, amongst others. In some embodiments, abinder material may be applied to a fiber slurry prior to introducingthe slurry into a headbox. For example, the binder material may beintroduced (e.g., injected) into the fiber slurry and impregnated withand/or precipitated on to the fibers. In some embodiments, a binderresin may be added to a layer by a solvent saturation process.

In other embodiments, a non-wet laid process is used to form one or morelayers of a media. For example, in a non-wet laid process, an air laidprocess or a carding process may be used. For example, in an air laidprocess, fibers may be mixed while air is blown onto a conveyor, and abinder is then applied. In a carding process, in some embodiments, thefibers are manipulated by rollers and extensions (e.g., hooks, needles)associated with the rollers prior to application of the binder. In somecases, forming the layers through a non-wet laid process may be moresuitable for the production of a highly porous media. The non-wet layermay be impregnated (e.g., via saturation, spraying, etc.) with anysuitable binder resin, as discussed above.

During or after formation of a layer, the layer may be further processedaccording to a variety of known techniques. Optionally, additionallayers can be formed and/or added to a layer using processes such aslamination, thermo-dot bonding, ultrasonic, calendering, glue-web,co-pleating, or collation. For example, in some cases, two layers areformed into a composite article by a wet laid process as describedabove, and the composite article is then combined with another layer byany suitable process (e.g., lamination, co-pleating, or collation). Inanother example, more than one layer (e.g., meltblown layers) may bejoined together by thermo-dot bonding, calendering, a glue web, orultrasonic processes to form a layer (e.g., the second layer). It can beappreciated that a layer formed by the processes described herein may besuitably tailored not only based on the components of each layer, butalso according to the effect of using multiple layers of varyingproperties in appropriate combination to form a layer or filter mediahaving the characteristics described herein.

In some embodiments, further processing may involve pleating the layerand/or the filter media. For instance, two layers may be joined by aco-pleating process. In some cases, the filter media, or various layersthereof, may be suitably pleated by forming score lines at appropriatelyspaced distances apart from one another, allowing the filter media to befolded. It should be appreciated that any suitable pleating techniquemay be used.

In some embodiments, a filter media can be post-processed such assubjected to a corrugation process to increase surface area within theweb. In other embodiments, a filter media may be embossed.

As described herein, in some embodiments, two or more layers (e.g., thefirst, second, third, and/or fourth layers) in the filter media may beformed separately, and joined by any suitable method such as lamination,collation, thermo-dot bonding, ultrasonic processes (e.g.,ultrasonically point bonded together), calendering, glue-web, or by useof adhesives. For instance, the third layer (e.g., a support layer) maybe joined to the second layer (e.g. an efficiency layer) usingthermo-dot bonding and an adhesive (e.g., spray or spinner). In somecases, the layers may be ultrasonically bonded together (e.g.,ultrasonically point bonded together). In other cases, the layers may becalendered together. Calendering may involve, for example, compressingtwo or more layers together using calender rolls under a particularlinear pressure, temperature, and line speed.

Two or more layers and/or sub-layers may be formed using differentprocesses, or the same process. For example, each of the layers may beindependently formed by a wet laid process, a non-wet laid process, aspinning process, a meltblown process, electrospun or any other suitableprocess. In some embodiments, two or more layers may be formed by thesame process (e.g., a wet laid process, a non-wet laid process, such asa spinning process, a meltblown process, or any other suitable process).In some instances, the two or more layers may be formed simultaneously.

In some embodiments, as described herein, a layer may include fibersformed from a meltblown process. In embodiments in which the filtermedia includes a meltblown layer, the meltblown layer may have one ormore characteristics described in commonly-owned U.S. Patent PublicationNo. 2009/0120048, entitled “Meltblown Filter Medium”, which is based onU.S. patent application Ser. No. 12/266,892, filed on May 14, 2009, andcommonly-owned U.S. application Ser. No. 12/971,539, entitled “FineFiber Filter Media and Processes”, filed on Dec. 17, 2010, each of whichis incorporated herein by reference in its entirety for all purposes. Inother embodiments, a layer may be formed via other suitable processessuch as meltspun, melt electrospinning and/or liquid electrospinningprocesses.

As described herein, a layer in the filter media may include a pluralityof perforations. In general the plurality of perforations may be formedby any suitable process. For instance, for a dry web, a plurality ofperforations may be formed by a thermo-mechanical process (e.g.,thermo-dot bonder) or a mechanical process (e.g., puncture orhydro-entangling). For a wet web, for example, a plurality ofperforations may be formed by using a perforated Dandy-roll or byhydro-entangling. In a thermo-dot bonder, a thermo-mechanical elementapplies heat and force to a layer to create perforations. Puncture andDandy roll processes involve the application of mechanical force on awet layer during drying to make the perforations. Hydro-entangling makesperforations in a layer through the application of hydro-mechanicalforce on a wet or dry layer. In some cases, the application of thermalenergy (e.g., a laser) can be used to form perforations.

The filter media described herein can be incorporated into a variety offilter elements for use in various applications including hydraulic andnon-hydraulic filtration applications. Exemplary uses of hydraulicfilters (e.g., high-, medium-, and low-pressure specialty filters)include mobile and industrial filters. Exemplary uses of non-hydraulicfilters include fuel filters (e.g., ultra-low sulfur diesel), oilfilters (e.g., lube oil filters or heavy duty lube oil filters),chemical processing filters, industrial processing filters, medicalfilters (e.g., filters for blood), air filters (e.g., heavy duty airfilters, automotive air filters, HVAC filters, HEPA filters), and waterfilters. In some embodiments, a number of layers of filter media may bewrapped around an inner substrate (e.g., a synthetic or metal core) toform a wrapped filter. For example, a wrapped filter may include between5 and 10 layers of filter media wrapped around the inner substrate. Insome cases, filter media described herein can be used as filter mediafor coalescing applications (e.g., using a wrapped filter). For example,such filter media may be used to remove oil from compressed air, or toremove water from fuel. In some embodiments, the third layersubstantially supports the filter element, such that an additionalsupport layer, such as a plastic or metallic net, wire, or mesh, isabsent from the filter media or filter element.

The filter elements may have the same property values as those notedabove in connection with the filter media. For example, the above-notedbasis weights, dust holding capacities, efficiencies of the filter mediamay also be found in filter elements.

During use, the filter media mechanically trap particles on or in thelayers as fluid flows through the filter media. The filter media neednot be electrically charged to enhance trapping of contamination. Thus,in some embodiments, the filter media are not electrically charged.However, in some embodiments, the filter media may be electricallycharged.

EXAMPLES Example 1

A filter media having four layers and the general configuration shown inFIG. 3 was fabricated.

The first layer (e.g., a capacity layer) included a multi-layer gradientstructure that was used to enhance the dust holding capacity of thefilter media. The first layer included three sub-layers, each sub-layerhaving a basis weight of about 30 gsm. The air permeabilities of thethree sub-layers were about 300 L/m²sec, about 400 L/m²sec, and about400 L/m²sec, respectively. The first layer was formed from polyesterfibers having fiber diameters from about 1 to about 4 microns. The firstlayer was formed by a meltblown process.

Adjacent the first layer was a second layer (e.g., an efficiency layer)used to enhance the particle capture efficiency of the filter media. Thesecond layer was a meltblown layer having a basis weight of about 20g/m². The second layer was formed of polybutylene terephthalate fibershaving an average fiber diameter of between about 0.2 microns and about0.5 microns. The air permeability of the second layer was about 110L/m²sec. The mean flow pore size was about 4 microns.

Adjacent the second layer was a fourth layer (e.g., a spacer layer) thatacted as a spacer between the second and third layers. The fourth layerwas a spunbond layer having a basis weight of about 15 gsm. The fourthlayer was formed of polybutylene terephthalate fibers having an averagediameter of about 10 to about 15 microns.

Adjacent the fourth layer on the opposite side of the second layer was athird layer (e.g., a support layer). The third layer was included toprovide structural support to the filter media. The third layer wasformed of cellulose fibers (a combination of a mercerized softwoodfibers and non-mercerized softwood fibers) and was impregnated with aphenolic resin. The third layer did not include perforations. The thirdlayer had a thickness of about 0.3 mm, a mean flow pore size of about 60microns, and had an air permeability of about 400 L/m²sec. The thirdlayer had a dry Mullen burst strength of about 50 kPa (prior to beingimpregnated with the phenolic resin).

The first, second, and fourth layers were point bonded together. Theselayers were then bonded to the third layer using a hot-melt adhesive.

The filter media had an initial efficiency (4 micron particles) of about99.0%, a beta ratio of about 100, and a dust holding capacity of about225 g/m² as measured according to the standard ISO 19438. The ISO 4020lifetime of the filter media was quite desirable. Notably, theefficiency of the filter media increased by about 2.3 times compared toComparative Example 1, described below. Additionally, the dust holdingcapacity improved by greater than 25% and the filter lifetime improvedby greater than 375%, compared to Comparative Example 1. The filtermedia in this example did not include any glass fibers.

Comparative Example 1

A filter media was fabricated by spray bonding a single meltblown layerincluding synthetic fibers onto a wet laid composite layer including amixture of cellulose and microglass fibers. The filter media had a basisweight of about 300 g/m² and a thickness of about 1 mm.

The filter media had an air permeability of about 2 CFM/ft², an initialefficiency (of 4 micron particles) of about 97.7%, and a dust holdingcapacity of about 175 g/m² as measured according to the standard ISO19438.

Example 2

A filter media similar to the one described in Example 1 was fabricated,except the second, efficiency layer included two second layers (i.e.,two sub-layers, each sub-layer having the construction of the secondlayer described in Example 1), which were used to enhance the particlecapture efficiency of the filter media. The two sub-layers of theefficiency layer included polybutylene terephthalate fibers formed by ameltblown process and the sub-layers were combined by point bonding. Thesecond layer had a mean pore flow size of about 3.4 microns. The filtermedia had an initial efficiency (of 4 micron particles) of about 99.75%,a beta ratio of about 400, and a dust holding capacity of about 275 g/m²as measured according to the standard ISO 19438.

Example 3

A filter media similar to that described in Example 1 was fabricatedexcept for the composition of the third layer, and the presence ofperforations in the third layer of this example. The third layer wasformed of cellulose fibers (a combination of a hardwood fibers andsoftwood fibers) known for imparting high structural strength to thefinal paper or nonwoven media. The layer was impregnated with a phenolicresin. The perforations in the third layer had a length of about 1.5 mmand a width of about 1.0 mm. The third layer had about 5% perforationcoverage. The air permeability of the third layer was about 900 L/m²sec.Prior to being perforated, the third layer had a mean flow pore size ofabout 10 microns.

The filter media provided about a 230% increase in air-permeability(e.g., a lower resistance) compared to the filter media of Example 1 dueto the presence of the perforations in the third layer. There was nosubstantially change (within variance) for dust holding capacity for thefilter media in this example compared to the filter media of Example 1.Additionally, the filter media in this example had an increase inlifetime of greater than 50% at the same dust holding capacityperformance compared to the media of Example 1. The increase in lifetimewas most likely due to the lowered resistance of the media (as a resultof the presence of perforations in the third layer) compared to themedia of Example 1.

Furthermore, because specific fibers known for imparting high structuralstrength to the final paper or nonwoven media were used in the thirdlayer, the dry Mullen Burst strength of the third layer was about 340kPa (prior to being impregnated with the phenolic resin), significantlyhigher than that of the third layer of Example 1, which had a dry MullenBurst strength of about 50 kPa. The specific fibers which yield highstrength properties also formed a relatively tight pore structure inthis layer (e.g., a mean flow pore size of about 10 microns compared toabout 60 microns in the third layer of Example 1). However, the presenceof the perforations in the third layer in this example alleviated thehigh resistance across the layer, resulting in a high air permeability(e.g., about 900 L/m²sec compared to about 400 L/m²sec for the thirdlayer of Example 1).

Example 4

A filter media similar to that described in Example 3 was fabricatedexcept the third layer had about a 10% perforation coverage. The airpermeability of the third layer was about 1100 L/m²sec. There was nosubstantial change (within variance) for dust holding capacity for thefilter media in this example compared to the filter media of Example 1.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

What is claimed is:
 1. A filter media, comprising: a first layercomprising a first plurality of fibers, wherein the first layer has afirst air permeability and a first mean flow pore size; a second layercomprising a second plurality of fibers having an average fiber diameterof less than or equal to about 1 micron, wherein the second layer has asecond air permeability and a second mean flow pore size, and whereinthe second plurality of fibers are formed by a melt-blown process; and athird layer comprising a third plurality of fibers, wherein the thirdplurality of fibers comprises cellulose fibers, wherein the third layerhas a third air permeability and a third mean flow pore size, andwherein the third layer has a density of greater than or equal to about0.75 kg/m³ and less than or equal to about 1.25 kg/m³, wherein each ofthe first and third air permeabilities is higher than the second airpermeability and/or wherein each of the first and third mean flow poresizes is higher than the second mean flow pore size, wherein the firstlayer, the second layer, and the third layer are discrete layers, andwherein the second layer is positioned between the first and thirdlayers.
 2. The filter media of claim 1, wherein the first mean flow poresize is higher than the second mean flow pore size.
 3. The filter mediaof claim 1, wherein the second mean flow pore size is greater than orequal to about 1 micron and less than or equal to about 10 microns. 4.The filter media of claim 1, wherein the first plurality of fiberscomprises synthetic fibers.
 5. The filter media of claim 1, wherein thefirst layer has an air permeability of greater than or equal to about150 L/m² sec and less than or equal to about 900 L/m² sec.
 6. The filtermedia of claim 1, wherein the first layer comprises a multi-layeredstructure.
 7. The filter media of claim 1, wherein the filter mediaincludes less than or equal to about 2 wt % glass fibers.
 8. The filtermedia of claim 1, wherein the average fiber diameter of the secondplurality of fibers is greater than or equal to about 0.2 and less thanor equal to about 0.8 microns.
 9. The filter media of claim 1, whereinthe second layer comprises a multi-layered structure.
 10. The filtermedia of claim 1, wherein the second layer has an efficiency of greaterthan or equal to about 99% and less than or equal to about 99.99% for 4micron or larger particles, as measured by a Multipass Filter Testfollowing the ISO 19438 procedure at a BUGL of 50 mg/L, a face velocityof 0.06 cm/s, and a terminal pressure of 100 kPa.
 11. The filter mediaof claim 1, wherein the filter media has an air permeability of greaterthan or equal to about 50 L/m² sec and less than or equal to about 500L/m² sec.
 12. The filter media of claim 1, wherein the third pluralityof fibers has an average fiber diameter of greater than or equal toabout 20 microns and less than or equal to about 50 microns.
 13. Thefilter media of claim 1, wherein the third layer has an average weightpercentage of cellulose fibers of greater than or equal to about 40percent and less than or equal to about 100 percent.
 14. The filtermedia of claim 1, wherein the third layer comprises a plurality ofperforations.
 15. The filter media of claim 14, wherein the perforationscover greater than or equal to about 5% and less than or equal to about20% of the surface area of the third layer.
 16. The filter media ofclaim 1, wherein the third layer has a Mullen Burst strength of greaterthan or equal to about 200 kPa and less than or equal to about 300 kPa.17. The filter media of claim 1, wherein the third layer has an airpermeability of greater than or equal to about 400 L/m² sec and lessthan or equal to about 700 L/m2 sec.
 18. The filter media of claim 1,wherein the first air permeability is higher than the second airpermeability.
 19. The filter media of claim 1, wherein the third airpermeability is at least 20 times greater than the second airpermeability and/or the first air permeability.
 20. The filter media ofclaim 1 comprising a fourth layer, wherein the fourth layer is aspun-bond layer.
 21. The filter media of claim 1, wherein the thirdlayer has a pressure drop of less than or equal to about 30 Pa.
 22. Thefilter media of claim 14, wherein the plurality of perforations have anaverage diameter of greater than or equal to about 0.5 mm and less thanor equal to about 5 mm.
 23. The filter media of claim 1, wherein thefilter media is pleated.
 24. A filter element comprising the filtermedia of claim 1, wherein the third layer is upstream of the firstlayer.
 25. A filter element comprising the filter media of claim 1,wherein the third layer is downstream of the first layer.
 26. The filtermedia of claim 14, wherein the average periodicity of the plurality ofperforation is greater than or equal to about 5 mm and less than orequal to about 20 mm.
 27. The filter media of claim 14, wherein theplurality of perforations have an average protrusion length of greaterthan or equal to about 1 mm and less than or equal to about 5 mm. 28.The filter media of claim 1, wherein the filter media has an averagelifetime of greater than or equal to about 40 minutes and less than orequal to about 85 minutes as measured according to the standard ISO4020.
 29. The filter media of claim 20, wherein the fourth layer has anaverage thickness of less than or equal to about 0.3 mm.
 30. The filtermedia of claim 1, wherein the first layer comprises at least threesub-layers.
 31. The filter media of claim 1, wherein the first pluralityof fibers comprises meltblown synthetic fibers.
 32. The filter media ofclaim 1, wherein the first plurality of fibers has an average diameterof greater than or equal to 1 micron.
 33. A filter element including thefilter media of claim 1, wherein the filter element lacks a plastic ormetallic net, wire, or mesh support structure.
 34. A filter media,comprising: a first layer comprising a first plurality of fibers,wherein the first layer has a first air permeability and a first meanflow pore size; a second layer comprising a second plurality of fibershaving an average fiber diameter of less than or equal to about 1micron, wherein the second layer has a second air permeability and asecond mean flow pore size; and a third layer comprising a thirdplurality of fibers, wherein the third plurality of fibers comprisescellulose fibers, wherein the third layer has a third air permeabilityand a third mean flow pore size, and wherein the third layer comprises aplurality of perforations, wherein each of the first and third airpermeabilities is higher than the second air permeability and/or whereineach of the first and third mean flow pore sizes is higher than thesecond mean flow pore size, wherein the first layer, the second layer,and the third layer are discrete layers, and wherein the second layer ispositioned between the first and third layers.
 35. The filter media ofclaim 34, wherein the first mean flow pore size is higher than thesecond mean flow pore size.
 36. The filter media of claim 34, whereinthe second mean flow pore size is greater than or equal to about 1micron and less than or equal to about 10 microns.
 37. The filter mediaof claim 34, wherein the first and/or second plurality of fiberscomprises synthetic fibers.
 38. The filter media of claim 34, whereinthe first layer has an air permeability of greater than or equal toabout 150 L/m² sec and less than or equal to about 900 L/m² sec.
 39. Thefilter media of claim 34, wherein the first layer comprises amulti-layered structure.
 40. The filter media of claim 34, wherein thefilter media includes less than or equal to about 2 wt % glass fibers.41. The filter media of claim 34, wherein the average fiber diameter ofthe second plurality of fibers is greater than or equal to about 0.2 andless than or equal to about 0.8 microns.
 42. The filter media of claim34, wherein the second layer comprises a multi-layered structure. 43.The filter media of claim 34, wherein the second layer has an efficiencyof greater than or equal to about 99% and less than or equal to about99.99% for 4 micron or larger particles, as measured by a MultipassFilter Test following the ISO 19438 procedure at a BUGL of 50 mg/L, aface velocity of 0.06 cm/s, and a terminal pressure of 100 kPa.
 44. Thefilter media of claim 34, wherein the filter media has an airpermeability of greater than or equal to about 50 L/m² sec and less thanor equal to about 500 L/m² sec.
 45. The filter media of claim 34,wherein the third plurality of fibers has an average fiber diameter ofgreater than or equal to about 20 microns and less than or equal toabout 50 microns.
 46. The filter media of claim 34, wherein the thirdlayer has an average weight percentage of cellulose fibers of greaterthan or equal to about 40 percent and less than or equal to about 100percent.
 47. The filter media of claim 34, wherein the third layer has aMullen Burst strength of greater than or equal to about 200 kPa and lessthan or equal to about 300 kPa.
 48. The filter media of claim 34,wherein the third layer has an air permeability of greater than or equalto about 400 L/m² sec and less than or equal to about 700 L/m² sec. 49.The filter media of claim 34, wherein the first air permeability ishigher than the second air permeability.
 50. The filter media of claim34, wherein the third air permeability is at least 20 times greater thanthe second air permeability and/or the first air permeability.
 51. Thefilter media of claim 34 comprising a fourth layer, wherein the fourthlayer is a spun-bond layer.
 52. The filter media of claim 34, whereinthe third layer has a density of greater than or equal to about 0.75kg/m³ and less than or equal to about 1.25 kg/m³.
 53. The filter mediaof claim 34, wherein the third layer has a pressure drop of less than orequal to about 30 Pa.
 54. The filter media of claim 34, wherein thefilter media is pleated.
 55. A filter element comprising the filtermedia of claim 34, wherein the third layer is upstream of the firstlayer.
 56. A filter element comprising the filter media of claim 34,wherein the third layer is downstream of the first layer.
 57. The filtermedia of claim 34, wherein the average periodicity of the plurality ofperforation is greater than or equal to about 5 mm and less than orequal to about 20 mm.
 58. The filter media of claim 34, wherein thefilter media has an average lifetime of greater than or equal to about40 minutes and less than or equal to about 85 minutes as measuredaccording to the standard ISO
 4020. 59. The filter media of claim 51,wherein the fourth layer has an average thickness of less than or equalto about 0.3 mm.
 60. The filter media of claim 34, wherein the firstlayer comprises at least three sub-layers.
 61. The filter media of claim34, wherein the first plurality of fibers comprises meltblown syntheticfibers.
 62. The filter media of claim 34, wherein the first plurality offibers has an average diameter of greater than or equal to 1 micron. 63.A filter element including the filter media of claim 34, wherein thefilter element lacks a plastic or metallic net, wire, or mesh supportstructure.
 64. A filter media, comprising: a first layer comprising afirst plurality of fibers, wherein the first layer has a first airpermeability and a first mean flow pore size; a second layer comprisinga second plurality of fibers having an average fiber diameter of lessthan or equal to about 1 micron, wherein the second layer has a secondair permeability and a second mean flow pore size; and a third layercomprising a third plurality of fibers, wherein the third plurality offibers comprises cellulose fibers, wherein the third layer has a thirdair permeability and a third mean flow pore size, and wherein the thirdlayer has a density of greater than or equal to about 0.75 kg/m³ andless than or equal to about 1.25 kg/m³, wherein each of the first andthird air permeabilities is higher than the second air permeabilityand/or wherein each of the first and third mean flow pore sizes ishigher than the second mean flow pore size, wherein the first layer, thesecond layer, and the third layer are discrete layers, and wherein thesecond layer is positioned between the first and third layers.
 65. Thefilter media of claim 64, wherein the first mean flow pore size ishigher than the second mean flow pore size.
 66. The filter media ofclaim 64, wherein the second mean flow pore size is greater than orequal to about 1 micron and less than or equal to about 10 microns. 67.The filter media of claim 64, wherein the first and/or second pluralityof fibers comprises synthetic fibers.
 68. The filter media of claim 64,wherein the first layer has an air permeability of greater than or equalto about 150 L/m² sec and less than or equal to about 900 L/m² sec. 69.The filter media of claim 64, wherein the first layer comprises amulti-layered structure.
 70. The filter media of claim 64, wherein thefilter media includes less than or equal to about 2 wt % glass fibers.71. The filter media of claim 64, wherein the average fiber diameter ofthe second plurality of fibers is greater than or equal to about 0.2 andless than or equal to about 0.8 microns.
 72. The filter media of claim64, wherein the second layer comprises a multi-layered structure. 73.The filter media of claim 64, wherein the second layer has an efficiencyof greater than or equal to about 99% and less than or equal to about99.99% for 4 micron or larger particles, as measured by a MultipassFilter Test following the ISO 19438 procedure at a BUGL of 50 mg/L, aface velocity of 0.06 cm/s, and a terminal pressure of 100 kPa.
 74. Thefilter media of claim 64, wherein the filter media has an airpermeability of greater than or equal to about 50 L/m² sec and less thanor equal to about 500 L/m² sec.
 75. The filter media of claim 64,wherein the third plurality of fibers has an average fiber diameter ofgreater than or equal to about 20 microns and less than or equal toabout 50 microns.
 76. The filter media of claim 64, wherein the thirdlayer has an average weight percentage of cellulose fibers of greaterthan or equal to about 40 percent and less than or equal to about 100percent.
 77. The filter media of claim 64, wherein the third layercomprises a plurality of perforations, and wherein the perforationscover greater than or equal to about 5% and less than or equal to about20% of the surface area of the third layer.
 78. The filter media ofclaim 64, wherein the third layer has a Mullen Burst strength of greaterthan or equal to about 200 kPa and less than or equal to about 300 kPa.79. The filter media of claim 64, wherein the third layer has an airpermeability of greater than or equal to about 400 L/m² sec and lessthan or equal to about 700 L/m² sec.
 80. The filter media of claim 64,wherein the first air permeability is higher than the second airpermeability.
 81. The filter media of claim 64, wherein the third airpermeability is at least 20 times greater than the second airpermeability and/or the first air permeability.
 82. The filter media ofclaim 64 comprising a fourth layer, wherein the fourth layer is aspun-bond layer.
 83. The filter media of claim 64, wherein the thirdlayer has a pressure drop of less than or equal to about 30 Pa.
 84. Thefilter media of claim 64, wherein the third layer comprises a pluralityof perforations, and wherein the plurality of perforations have anaverage diameter of greater than or equal to about 0.5 mm and less thanor equal to about 5 mm.
 85. The filter media of claim 64, wherein thefilter media is pleated.
 86. A filter element comprising the filtermedia of claim 64, wherein the third layer is upstream of the firstlayer.
 87. A filter element comprising the filter media of claim 64,wherein the third layer is downstream of the first layer.
 88. The filtermedia of claim 64, wherein the third layer comprises a plurality ofperforations, and wherein the average periodicity of the plurality ofperforation is greater than or equal to about 5 mm and less than orequal to about 20 mm.
 89. The filter media of claim 64, wherein thethird layer comprises a plurality of perforations, and wherein theplurality of perforations have an average protrusion length of greaterthan or equal to about 1 mm and less than or equal to about 5 mm. 90.The filter media of claim 64, wherein the filter media has an averagelifetime of greater than or equal to about 40 minutes and less than orequal to about 85 minutes as measured according to the standard ISO4020.
 91. The filter media of claim 82, wherein the fourth layer has anaverage thickness of less than or equal to about 0.3 mm.
 92. The filtermedia of claim 64, wherein the first layer comprises at least threesub-layers.
 93. The filter media of claim 64, wherein the firstplurality of fibers comprises meltblown synthetic fibers.
 94. The filtermedia of claim 64, wherein the first plurality of fibers has an averagediameter of greater than or equal to 1 micron.
 95. A filter elementincluding the filter media of claim 64, wherein the filter element lacksa plastic or metallic net, wire, or mesh support structure.
 96. A filtermedia, comprising: a first layer comprising a first plurality of fibers,wherein the first layer has a first air permeability and a first meanflow pore size; a second layer comprising a second plurality of fibershaving an average fiber diameter of less than or equal to about 1micron, wherein the second layer has a second air permeability and asecond mean flow pore size; and a third layer comprising a thirdplurality of fibers, wherein the third plurality of fibers comprisescellulose fibers, wherein the third layer has a third air permeabilityand a third mean flow pore size, and wherein the third layer comprises aplurality of perforations, and wherein the perforations cover greaterthan or equal to about 5% and less than or equal to about 20% of thesurface area of the third layer, wherein each of the first and third airpermeabilities is higher than the second air permeability and/or whereineach of the first and third mean flow pore sizes is higher than thesecond mean flow pore size, wherein the first layer, the second layer,and the third layer are discrete layers, and wherein the second layer ispositioned between the first and third layers.
 97. A filter media,comprising: a first layer comprising a first plurality of fibers,wherein the first layer has a first air permeability and a first meanflow pore size; a second layer comprising a second plurality of fibershaving an average fiber diameter of less than or equal to about 1micron, wherein the second layer has a second air permeability and asecond mean flow pore size; and a third layer comprising a thirdplurality of fibers, wherein the third plurality of fibers comprisescellulose fibers, wherein the third layer has a third air permeabilityand a third mean flow pore size, and wherein the third layer comprises aplurality of perforations, and wherein the plurality of perforationshave an average diameter of greater than or equal to about 0.5 mm andless than or equal to about 5 mm, wherein each of the first and thirdair permeabilities is higher than the second air permeability and/orwherein each of the first and third mean flow pore sizes is higher thanthe second mean flow pore size, wherein the first layer, the secondlayer, and the third layer are discrete layers, and wherein the secondlayer is positioned between the first and third layers.
 98. A filtermedia, comprising: a first layer comprising a first plurality of fibers,wherein the first layer has a first air permeability and a first meanflow pore size; a second layer comprising a second plurality of fibershaving an average fiber diameter of less than or equal to about 1micron, wherein the second layer has a second air permeability and asecond mean flow pore size; and a third layer comprising a thirdplurality of fibers, wherein the third plurality of fibers comprisescellulose fibers, wherein the third layer has a third air permeabilityand a third mean flow pore size, and wherein the third layer comprises aplurality of perforations, and wherein the plurality of perforationshave an average protrusion length of greater than or equal to about 1 mmand less than or equal to about 5 mm, wherein each of the first andthird air permeabilities is higher than the second air permeabilityand/or wherein each of the first and third mean flow pore sizes ishigher than the second mean flow pore size, wherein the first layer, thesecond layer, and the third layer are discrete layers, and wherein thesecond layer is positioned between the first and third layers.